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 (40209)
A heap-use-after-free flaw was found in ImageMagick's RelinquishDCMInfo() function of dcm.c file. Rated high severity (CVSS 7.1), this vulnerability is no authentication required, low attack complexity. No vendor patch available.
A use-after-free flaw was found in the Linux kernel’s sound subsystem in the way a user triggers concurrent calls of PCM hw_params. Rated high severity (CVSS 7.0). This Use After Free vulnerability could allow attackers to access freed memory to execute arbitrary code or crash the application.
Redis is an in-memory database that persists on disk. Rated medium severity (CVSS 5.5), this vulnerability is low attack complexity. Public exploit code available.
NVIDIA Jetson Linux Driver Package contains a vulnerability in the Cboot ext4_mount function, where Insufficient validation of untrusted data may allow a highly privileged local attacker to cause an. Rated medium severity (CVSS 5.0). No vendor patch available.
NVIDIA Jetson Linux Driver Package contains a vulnerability in the Cboot blob_decompress function, where insufficient validation of untrusted data may allow a local attacker with elevated privileges. Rated medium severity (CVSS 4.6), this vulnerability is low attack complexity. No vendor patch available.
NVIDIA Jetson Linux Driver Package contains a vulnerability in the Cboot ext4_read_file function, where insufficient validation of untrusted data may allow a highly privileged local attacker to cause. Rated medium severity (CVSS 5.7), this vulnerability is low attack complexity. No vendor patch available.
NVIDIA Jetson Linux Driver Package contains a vulnerability in the Cboot module tegrabl_cbo.c, where, if TFTP is enabled, a local attacker with elevated privileges can cause a memory buffer overflow,. Rated medium severity (CVSS 5.6), this vulnerability is low attack complexity. No vendor patch available.
NVIDIA Jetson Linux Driver Package contains a vulnerability in the Cboot module tegrabl_cbo.c, where insufficient validation of untrusted data may allow a local attacker with elevated privileges to. Rated medium severity (CVSS 5.6), this vulnerability is low attack complexity. No vendor patch available.
A vulnerability in SonicOS CFS (Content filtering service) returns a large 403 forbidden HTTP response message to the source address when users try to access prohibited resource this allows an. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
Improper Restriction of TCP Communication Channel in HTTP/S inbound traffic from WAN to DMZ bypassing security policy until TCP handshake potentially resulting in Denial of Service (DoS) attack if a. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
chafa: NULL Pointer Dereference in function gif_internal_decode_frame at libnsgif.c:599 allows attackers to cause a denial of service (crash) via a crafted input file. Rated medium severity (CVSS 5.5), this vulnerability is no authentication required, low attack complexity. Public exploit code available.
IBM Security Identity Manager (IBM Security Verify Password Synchronization Plug-in for Windows AD 10.x) is vulnerable to a denial of service, caused by a heap-based buffer overflow in the Password. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
IBM Security Identity Manager (IBM Security Verify Password Synchronization Plug-in for Windows AD 10.x) is vulnerable to a denial of service, caused by a heap-based buffer overflow in the Password. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
A lack of rate limiting in the 'forgot password' feature of Zammad v5.1.0 allows attackers to send an excessive amount of reset requests for a legitimate user, leading to a possible Denial of Service. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. This Allocation of Resources Without Limits vulnerability could allow attackers to exhaust system resources through uncontrolled allocation.
A lack of password length restriction in Zammad v5.1.0 allows for the creation of extremely long passwords which can cause a Denial of Service (DoS) during password verification. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
A flaw was found in htmldoc commit 31f7804. Rated high severity (CVSS 7.8), this vulnerability is no authentication required, low attack complexity. Public exploit code available.
An access control issue in Zammad v5.0.3 allows attackers to write entries to the CTI caller log without authentication. Rated critical severity (CVSS 9.1), this vulnerability is remotely exploitable, no authentication required, low attack complexity. This Missing Authentication for Critical Function vulnerability could allow attackers to access critical functionality without authentication.
An issue has been discovered in GitLab affecting all versions starting from 11.9 before 14.5.4, all versions starting from 14.6.0 before 14.6.4, all versions starting from 14.7.0 before 14.7.1. Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
PJSIP is a free and open source multimedia communication library written in C. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
xpdf 4.03 has heap buffer overflow in the function readXRefTable located in XRef.cc. Rated medium severity (CVSS 5.5), this vulnerability is no authentication required, low attack complexity. Public exploit code available and no vendor patch available.
A Denial-of-Service (DoS) vulnerability was discovered in F-Secure Atlant whereby the fsicapd component used in certain F-Secure products while scanning larger packages/fuzzed files consume too much. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
HtmlUnit NekoHtml Parser before 2.61.0 suffers from a denial of service vulnerability. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
heap-use-after-free in GitHub repository radareorg/radare2 prior to 5.7.0. Rated medium severity (CVSS 5.5), this vulnerability is no authentication required, low attack complexity. Public exploit code available.
A denial of service vulnerability was reported in Lenovo Thin Installer prior to version 1.3.0039 that could trigger a system crash. Rated medium severity (CVSS 5.5), this vulnerability is low attack complexity. No vendor patch available.
Certain Neko-related HTML parsers allow a denial of service via crafted Processing Instruction (PI) input that causes excessive heap memory consumption. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
Dell iDRAC8 versions prior to 2.83.83.83 contain a denial of service vulnerability. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
Dell PowerEdge Server BIOS and Dell Precision Workstation 7910 and 7920 Rack BIOS contain an Improper SMM communication buffer verification vulnerability. Rated medium severity (CVSS 6.0), this vulnerability is low attack complexity. No vendor patch available.
A vulnerability in the Cisco Discovery Protocol of Cisco Unified Communications Manager (Unified CM) and Cisco Unified Communications Manager Session Management Edition (Unified CM SME) could allow. Rated medium severity (CVSS 6.5), this vulnerability is no authentication required, low attack complexity. No vendor patch available.
A vulnerability in the implementation of the Datagram TLS (DTLS) protocol in Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an. 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 packet processing functionality of Cisco TelePresence Collaboration Endpoint (CE) Software and Cisco RoomOS Software could allow an unauthenticated, remote attacker to cause a. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
An authenticated user may trigger an invariant assertion during command dispatch due to incorrect validation on the $external database. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, low attack complexity.
An issue was discovered on Olivetti d-COLOR MF3555 2XD_S000.002.271 devices. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.
Vulnerability in the Oracle Solaris product of Oracle Systems (component: Kernel). Rated medium severity (CVSS 4.0). No vendor patch available.
Vulnerability in the Oracle Solaris product of Oracle Systems (component: Kernel). Rated medium severity (CVSS 5.9), this vulnerability is low attack complexity. No vendor patch available.
Vulnerability in the MySQL Cluster product of Oracle MySQL (component: Cluster: General). Rated low severity (CVSS 2.9). No vendor patch available.
Vulnerability in the MySQL Cluster product of Oracle MySQL (component: Cluster: General). Rated low severity (CVSS 2.9). No vendor patch available.
Vulnerability in the MySQL Cluster product of Oracle MySQL (component: Cluster: General). Rated low severity (CVSS 2.9). No vendor patch available.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Optimizer). 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: Optimizer). Rated medium severity (CVSS 5.5), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the Oracle Banking Payments product of Oracle Financial Services Applications (component: Infrastructure). Rated medium severity (CVSS 5.9), this vulnerability is remotely exploitable. No vendor patch available.
Vulnerability in the Oracle Banking Trade Finance product of Oracle Financial Services Applications (component: Infrastructure). Rated medium severity (CVSS 5.9), this vulnerability is remotely exploitable. No vendor patch available.
Vulnerability in the Oracle Banking Treasury Management product of Oracle Financial Services Applications (component: Infrastructure). Rated medium severity (CVSS 5.9), this vulnerability is remotely exploitable. No vendor patch available.
Vulnerability in the Oracle FLEXCUBE Universal Banking product of Oracle Financial Services Applications (component: Infrastructure). Rated medium severity (CVSS 5.9), this vulnerability is remotely exploitable. No vendor patch available.
Vulnerability in the Oracle VM VirtualBox product of Oracle Virtualization (component: Core). Rated medium severity (CVSS 6.5), 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 6.7), this vulnerability is low attack complexity. No vendor patch available.
Vulnerability in the JD Edwards EnterpriseOne Tools product of Oracle JD Edwards (component: Business Logic Infra SEC). Rated high severity (CVSS 8.2), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
Vulnerability in the Oracle Solaris product of Oracle Systems (component: Kernel). Rated medium severity (CVSS 5.5), this vulnerability is 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: Optimizer). 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: Group Replication Plugin). Rated medium severity (CVSS 6.5), 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: InnoDB). Rated medium severity (CVSS 4.4), this vulnerability is remotely exploitable. No vendor patch available.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: DDL). Rated medium severity (CVSS 4.4), this vulnerability is remotely exploitable. No vendor patch available.
Vulnerability in the Oracle Java SE, Oracle GraalVM Enterprise Edition product of Oracle Java SE (component: Libraries). Rated low severity (CVSS 3.7), this vulnerability is remotely exploitable, no authentication required.
Vulnerability in the Oracle WebLogic Server product of Oracle Fusion Middleware (component: Core). 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: Optimizer). 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: 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: 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: 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: 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: FTS). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the Oracle Java SE, Oracle GraalVM Enterprise Edition product of Oracle Java SE (component: JAXP). Rated medium severity (CVSS 5.3), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: DDL). Rated medium severity (CVSS 5.5), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the Oracle Communications Billing and Revenue Management product of Oracle Communications Applications (component: Connection Manager). Rated high severity (CVSS 8.3), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the MySQL Server product of Oracle MySQL (component: InnoDB). Rated low severity (CVSS 2.7), 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 5.0), this vulnerability is remotely exploitable. 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: Replication). 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: 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 4.9), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
http-swagger is an open source wrapper to automatically generate RESTful API documentation with Swagger 2.0. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. This Uncontrolled Resource Consumption vulnerability could allow attackers to cause denial of service by exhausting system resources.
PyPDF2 is an open source python PDF library capable of splitting, merging, cropping, and transforming the pages of PDF files. Rated medium severity (CVSS 5.5), this vulnerability is no authentication required, low attack complexity. Public exploit code available.
An issue was discovered in in bwm-ng v0.6.2. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available.
NULL Pointer Dereference in GitHub repository radareorg/radare2 prior to 5.6.8. Rated medium severity (CVSS 5.5), this vulnerability is no authentication required, low attack complexity. Public exploit code available.
YARP Denial of Service Vulnerability. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
Windows Secure Channel Denial of Service Vulnerability. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
.NET Framework Denial of Service Vulnerability. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
Windows Lightweight Directory Access Protocol (LDAP) Denial of Service Vulnerability. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
Windows Cluster Shared Volume (CSV) Denial of Service Vulnerability. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Microsoft Defender Denial of Service Vulnerability. Rated medium severity (CVSS 5.5), this vulnerability is no authentication required, low attack complexity. No vendor patch available.
Windows Cluster Shared Volume (CSV) Denial of Service Vulnerability. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Windows Cluster Shared Volume (CSV) Denial of Service Vulnerability. Rated medium severity (CVSS 5.5), this vulnerability is low attack complexity. No vendor patch available.
Windows Hyper-V Denial of Service Vulnerability. Rated medium severity (CVSS 6.5), this vulnerability is low attack complexity. No vendor patch available.
A denial of service vulnerability exists in the parseNormalModeParameters functionality of MZ Automation GmbH libiec61850 1.5.0. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available.
A vulnerability in the integrated wireless access point (AP) packet processing of the Cisco 1000 Series Connected Grid Router (CGR1K) could allow an unauthenticated, adjacent attacker to cause a. Rated medium severity (CVSS 6.5), this vulnerability is no authentication required, low attack complexity. No vendor patch available.
A vulnerability in the implementation of the Border Gateway Protocol (BGP) Ethernet VPN (EVPN) functionality in Cisco IOS XR Software could allow an unauthenticated, remote attacker to cause a denial. Rated medium severity (CVSS 6.8), this vulnerability is remotely exploitable, no authentication required. No vendor patch available.
Multiple vulnerabilities that affect Cisco Catalyst Digital Building Series Switches and Cisco Catalyst Micro Switches could allow an attacker to execute persistent code at boot time or to. Rated medium severity (CVSS 6.8), this vulnerability is no authentication required, low attack complexity. No vendor patch available.
A vulnerability in the NETCONF process of Cisco SD-WAN vEdge Routers could allow an authenticated, local attacker to cause an affected device to run out of memory, resulting in a denial of service. Rated medium severity (CVSS 5.5), this vulnerability is low attack complexity. No vendor patch available.
A vulnerability in the data plane microcode of Lightspeed-Plus line cards for Cisco ASR 9000 Series Aggregation Services Routers could allow an unauthenticated, remote attacker to cause the line card. Rated high severity (CVSS 8.6), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.