Denial of Service
Denial of Service attacks render applications or systems unavailable by overwhelming resources or triggering failure conditions.
How It Works
Denial of Service attacks render applications or systems unavailable by overwhelming resources or triggering failure conditions. Attackers exploit asymmetry: minimal attacker effort produces disproportionate resource consumption on the target. Application-level attacks use specially crafted inputs that trigger expensive operations—a regex engine processing malicious patterns can backtrack exponentially, or XML parsers recursively expand entities until memory exhausts. Network-level attacks flood targets with connection requests or amplify traffic through reflection, but application vulnerabilities often provide the most efficient attack surface.
The attack typically begins with reconnaissance to identify resource-intensive operations or unprotected endpoints. For algorithmic complexity attacks, adversaries craft inputs hitting worst-case performance—hash collision inputs filling hash tables with collisions, deeply nested JSON triggering recursive parsing, or pathological regex patterns like (a+)+b against strings of repeated 'a' characters. Resource exhaustion attacks open thousands of connections, upload massive files to unbounded storage, or trigger memory leaks through repeated operations. Crash-based attacks target error handling gaps: null pointer dereferences, unhandled exceptions in parsers, or assertion failures that terminate processes.
Impact
- Service unavailability preventing legitimate users from accessing applications during attack duration
- Revenue loss from downtime in e-commerce, SaaS platforms, or transaction processing systems
- Cascading failures as resource exhaustion spreads to dependent services or database connections pool out
- SLA violations triggering financial penalties and damaging customer trust
- Security team distraction providing cover for data exfiltration or intrusion attempts running concurrently
Real-World Examples
CVE-2018-1000544 in Ruby's WEBrick server allowed ReDoS through malicious HTTP headers containing specially crafted patterns that caused the regex engine to backtrack exponentially, freezing request processing threads. A single attacker could saturate all available workers.
Cloudflare experienced a global outage in 2019 when a single WAF rule containing an unoptimized regex hit pathological cases on legitimate traffic spikes. The .*(?:.*=.*)* pattern exhibited catastrophic backtracking, consuming CPU cycles across their edge network until the rule was disabled.
CVE-2013-1664 demonstrated XML bomb vulnerabilities in Python's XML libraries. Attackers uploaded XML documents with nested entity definitions-each entity expanding to ten copies of the previous level. A 1KB upload could expand to gigabytes in memory during parsing, crashing applications instantly.
Mitigation
- Strict input validation enforcing size limits, complexity bounds, and nesting depth restrictions before processing
- Request rate limiting per IP address, API key, or user session with exponential backoff
- Timeout enforcement terminating operations exceeding reasonable execution windows (typically 1-5 seconds)
- Resource quotas limiting memory allocation, CPU time, and connection counts per request or tenant
- Regex complexity analysis using linear-time algorithms or sanitizing patterns to eliminate backtracking
- Circuit breakers automatically rejecting requests when error rates or latency thresholds indicate degradation
- Load balancing and autoscaling distributing traffic across instances with automatic capacity expansion
Recent CVEs (40218)
A Race Condition vulnerability in Juniper Networks Junos OS LLDP implementation allows an attacker to cause LLDP to crash leading to a Denial of Service (DoS). Rated medium severity (CVSS 6.5), this vulnerability is no authentication required, low attack complexity. No vendor patch available.
An improper use of a validation framework when processing incoming genuine BGP packets within Juniper Networks RPD (routing protocols process) daemon allows an attacker to crash RPD thereby causing a. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
GNU LibreDWG before 0.11 allows NULL pointer dereferences via crafted input files. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.
A vulnerability in the deep packet inspection (DPI) engine of Cisco SD-WAN vEdge Routers could allow an unauthenticated, adjacent attacker to cause a denial of service (DoS) condition on an affected. Rated medium severity (CVSS 6.5), this vulnerability is no authentication required, low attack complexity. No vendor patch available.
A vulnerability in the web-based management interface of Cisco SD-WAN vManage Software could allow an authenticated, remote attacker to consume excessive system memory and cause a denial of service. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
A vulnerability in the deep packet inspection (DPI) engine of Cisco SD-WAN vEdge Routers could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
A vulnerability in the Secure Sockets Layer (SSL) VPN feature for Cisco Small Business RV VPN Routers could allow an unauthenticated, remote attacker to cause the device to unexpectedly restart,. Rated high severity (CVSS 8.6), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
A vulnerability in the Secure Sockets Layer (SSL) VPN feature of Cisco Small Business RV340, RV340W, RV345, and RV345P Dual WAN Gigabit VPN Routers could allow an unauthenticated, remote attacker to. Rated critical severity (CVSS 9.8), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
A vulnerability in Cisco SD-WAN Solution Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition. Rated high severity (CVSS 8.6), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
An issue was discovered in ajv.validate() in Ajv (aka Another JSON Schema Validator) 6.12.2. Rated medium severity (CVSS 5.6), this vulnerability is remotely exploitable, no authentication required. No vendor patch available.
In Synergy before version 1.12.0, a Synergy server can be crashed by receiving a kMsgHelloBack packet with a client name length set to 0xffffffff (4294967295) if the servers memory is less than 4 GB. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the Oracle Enterprise Communications Broker product of Oracle Communications Applications (component: WebGUI). Rated medium severity (CVSS 5.8), this vulnerability is remotely exploitable, no authentication required. No vendor patch available.
Vulnerability in the Oracle Enterprise Communications Broker product of Oracle Communications Applications (component: WebGUI). Rated medium severity (CVSS 6.3), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the Oracle VM VirtualBox product of Oracle Virtualization (component: Core). Rated medium severity (CVSS 4.4), this vulnerability is low attack complexity. No vendor patch available.
Vulnerability in the Oracle VM VirtualBox product of Oracle Virtualization (component: Core). Rated medium severity (CVSS 4.4), this vulnerability is low attack complexity. No vendor patch available.
Vulnerability in the Oracle VM VirtualBox product of Oracle Virtualization (component: Core). Rated medium severity (CVSS 5.0), this vulnerability is low attack complexity. No vendor patch available.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Security: Privileges). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Optimizer). Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the Oracle CRM Technical Foundation product of Oracle E-Business Suite (component: Preferences). Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
Vulnerability in the Oracle Financial Services Analytical Applications Infrastructure product of Oracle Financial Services Applications (component: Infrastructure). Rated medium severity (CVSS 6.3), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Locking). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Optimizer). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Security: Roles). Rated medium severity (CVSS 5.5), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Security: Roles). Rated medium severity (CVSS 5.5), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the Oracle Coherence product of Oracle Fusion Middleware (component: CacheStore). Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Options). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Security: Audit). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: JSON). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the MySQL Server product of Oracle MySQL (component: InnoDB). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: DML). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Parser). Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Optimizer). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the Oracle WebCenter Portal product of Oracle Fusion Middleware (component: Composer). Rated high severity (CVSS 8.6), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
Vulnerability in the Oracle Business Intelligence Enterprise Edition product of Oracle Fusion Middleware (component: Analytics Web Answers). Rated high severity (CVSS 8.6), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Optimizer). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the Oracle iLearning product of Oracle iLearning (component: Assessment Manager). Rated high severity (CVSS 8.2), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Audit Plug-in). Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the Oracle WebLogic Server product of Oracle Fusion Middleware (component: Web Container). Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Security: Privileges). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the Oracle Communications Session Border Controller product of Oracle Communications Applications (component: System Admin). Rated high severity (CVSS 8.2), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the Java SE, Java SE Embedded product of Oracle Java SE (component: Libraries). Rated low severity (CVSS 3.7), this vulnerability is remotely exploitable, no authentication required.
Vulnerability in the Java SE, Java SE Embedded product of Oracle Java SE (component: Libraries). Rated low severity (CVSS 3.7), this vulnerability is remotely exploitable, no authentication required.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: UDF). Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: DML). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the MySQL Server product of Oracle MySQL (component: InnoDB). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Replication). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the Oracle Unified Directory product of Oracle Fusion Middleware (component: Security). Rated high severity (CVSS 8.1), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the Java SE product of Oracle Java SE (component: ImageIO). Rated medium severity (CVSS 5.3), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
Vulnerability in the MySQL Client product of Oracle MySQL (component: C API). Rated medium severity (CVSS 5.3), this vulnerability is remotely exploitable. No vendor patch available.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Optimizer). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the Oracle Solaris product of Oracle Systems (component: Device Driver Utility). Rated medium severity (CVSS 5.0). No vendor patch available.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: DML). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Optimizer). Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the Oracle Solaris product of Oracle Systems (component: Packaging Scripts). Rated medium severity (CVSS 5.5), this vulnerability is low attack complexity. No vendor patch available.
Prototype pollution attack when using _.zipObjectDeep in lodash before 4.17.20. Rated high severity (CVSS 7.4), this vulnerability is remotely exploitable, no authentication required. Public exploit code available.
A denial of service vulnerability exists when the .NET implementation of Bond improperly parses input, aka 'Bond Denial of Service Vulnerability'. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. This Unrestricted File Upload vulnerability could allow attackers to upload malicious files that can be executed on the server.
An elevation of privilege vulnerability exists when Windows Error Reporting manager improperly handles a process crash, aka 'Windows Error Reporting Manager Elevation of Privilege Vulnerability'. Rated high severity (CVSS 7.8), this vulnerability is low attack complexity.
A denial of service vulnerability exists in the way that the WalletService handles files, aka 'Windows WalletService Denial of Service Vulnerability'. Rated high severity (CVSS 7.1), this vulnerability is low attack complexity.
This security update corrects a denial of service in the Local Security Authority Subsystem Service (LSASS) caused when an authenticated attacker sends a specially crafted authentication request, aka. Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity.
In freewvs before 0.1.1, a directory structure of more than 1000 nested directories can interrupt a freewvs scan due to Python's recursion limit and os.walk(). Rated low severity (CVSS 3.3), this vulnerability is low attack complexity. This Uncontrolled Resource Consumption vulnerability could allow attackers to cause denial of service by exhausting system resources.
In freewvs before 0.1.1, a user could create a large file that freewvs will try to read, which will terminate a scan process. Rated low severity (CVSS 3.3), this vulnerability is low attack complexity. This Uncontrolled Resource Consumption vulnerability could allow attackers to cause denial of service by exhausting system resources.
The payload length in a WebSocket frame was not correctly validated in Apache Tomcat 10.0.0-M1 to 10.0.0-M6, 9.0.0.M1 to 9.0.36, 8.5.0 to 8.5.56 and 7.0.27 to 7.0.104. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
An h2c direct connection to Apache Tomcat 10.0.0-M1 to 10.0.0-M6, 9.0.0.M5 to 9.0.36 and 8.5.1 to 8.5.56 did not release the HTTP/1.1 processor after the upgrade to HTTP/2. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. This Memory Leak vulnerability could allow attackers to exhaust available memory leading to denial of service.
A vulnerability has been identified in Opcenter Execution Discrete (All versions < V3.2), Opcenter Execution Foundation (All versions < V3.2), Opcenter Execution Process (All versions < V3.2),. Rated high severity (CVSS 8.2), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
A vulnerability has been identified in SIMATIC S7-200 SMART CPU family (All versions >= V2.2 < V2.5.1). Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
IBM QRadar SIEM 7.3 and 7.4 could allow an authenticated user to cause a denial of service of the qflow process by sending a malformed sflow command. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, low attack complexity.
A CSRF issue in the /goform/SysToolReboot endpoint of Tenda AC15 AC1900 version 15.03.05.19 allows remote attackers to reboot the device and cause denial of service via a payload hosted by an. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.
Appweb before 7.2.2 and 8.x before 8.1.0, when built with CGI support, mishandles an HTTP request with a Range header that lacks an exact range. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
Improper input validation in Citrix ADC and Citrix Gateway versions before 11.1-63.9 and 12.0-62.10 allows unauthenticated users to perform a denial of service attack. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
An issue was discovered in Yubico libykpiv before 2.1.0. Rated medium severity (CVSS 4.6), this vulnerability is no authentication required, low attack complexity. Public exploit code available and no vendor patch available.
When browsing a malicious page, a race condition in our SharedWorkerService could occur and lead to a potentially exploitable crash. Rated medium severity (CVSS 5.3), this vulnerability is remotely exploitable, no authentication required. Public exploit code available and no vendor patch available.
Incorrect handling of Upgrade header with the value websocket leads in crashing of containers hosting sockjs apps. Rated medium severity (CVSS 5.3), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available.
An integer underflow vulnerability in the dnsproxyd component of the PAN-OS management interface allows authenticated administrators to issue a command from the command line interface that causes the. Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
A memory leak in Openthread's wpantund versions up to commit 0e5d1601febb869f583e944785e5685c6c747be7, when used in an environment where wpanctl is directly interfacing with the control driver (eg:. Rated medium severity (CVSS 5.5), this vulnerability is low attack complexity.
A flaw was found in all Samba versions before 4.10.17, before 4.11.11 and before 4.12.4 in the way it processed NetBios over TCP/IP. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
A NULL pointer dereference, or possible use-after-free flaw was found in Samba AD LDAP server in versions before 4.10.17, before 4.11.11 and before 4.12.4. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
An issue was discovered in Xen through 4.13.x, allowing Intel guest OS users to gain privileges or cause a denial of service because of non-atomic modification of a live EPT PTE. Rated high severity (CVSS 7.8).
An issue was discovered in Xen through 4.13.x, allowing guest OS users to cause a host OS crash because of incorrect error handling in event-channel port allocation. Rated medium severity (CVSS 6.5), this vulnerability is low attack complexity. No vendor patch available.
An issue was discovered in Xen through 4.13.x, allowing x86 Intel HVM guest OS users to cause a host OS denial of service or possibly gain privileges because of insufficient cache write-back under. Rated high severity (CVSS 8.8), this vulnerability is low attack complexity. This Uncontrolled Resource Consumption vulnerability could allow attackers to cause denial of service by exhausting system resources.
An issue was discovered in Xen through 4.13.x, allowing Arm guest OS users to cause a hypervisor crash because of a missing alignment check in VCPUOP_register_vcpu_info. Rated medium severity (CVSS 6.5), this vulnerability is low attack complexity. This Buffer Overflow vulnerability could allow attackers to corrupt memory to execute arbitrary code or crash the application.
An issue was discovered in Xen through 4.13.x, allowing x86 HVM guest OS users to cause a hypervisor crash. Rated medium severity (CVSS 6.5), this vulnerability is low attack complexity. This Buffer Overflow vulnerability could allow attackers to corrupt memory to execute arbitrary code or crash the application.
TCP/IP function included in the firmware of Mitsubishi Electric GOT2000 series (CoreOS with version -Y and earlier installed in GT27 Model, GT25 Model, and GT23 Model) contains a null pointer. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
HUAWEI Mate 30 with versions earlier than 10.1.0.150(C00E136R5P3) have a use after free vulnerability. Rated high severity (CVSS 7.8), this vulnerability is no authentication required, low attack complexity. No vendor patch available.
A use-after-free flaw was found in all samba LDAP server versions before 4.10.17, before 4.11.11, before 4.12.4 used in a AC DC configuration. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Dell EMC PowerStore versions prior to 1.0.1.0.5.002 contain a vulnerability that exposes test interface ports to external network. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
ChangXiang 8 Plus with versions earlier than 9.1.0.136(C00E121R1P6T8) have a denial of service vulnerability. Rated medium severity (CVSS 5.3), this vulnerability is no authentication required. No vendor patch available.
A flaw was found in the AD DC NBT server in all Samba versions before 4.10.17, before 4.11.11 and before 4.12.4. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
The parse_report() function in whoopsie.c in Whoopsie through 0.2.69 mishandles memory allocation failures, which allows an attacker to cause a denial of service via a malformed crash file. Rated medium severity (CVSS 5.5), this vulnerability is no authentication required, low attack complexity. Public exploit code available and no vendor patch available.
In Wireshark 3.2.0 to 3.2.4, the GVCP dissector could go into an infinite loop. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
In QEMU 4.2.0, a MemoryRegionOps object may lack read/write callback methods, leading to a NULL pointer dereference. Rated low severity (CVSS 2.3), this vulnerability is low attack complexity.