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 (40219)
A vulnerability in the VPN System Logging functionality for Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a memory leak that can deplete. Rated high severity (CVSS 8.6), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
A vulnerability in how Cisco Firepower Threat Defense (FTD) Software handles session timeouts for management connections could allow an unauthenticated, remote attacker to cause a buildup of remote. Rated medium severity (CVSS 5.3), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
A vulnerability in the generic routing encapsulation (GRE) tunnel decapsulation feature of Cisco Firepower Threat Defense (FTD) 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.
A flaw was found when using samba as an Active Directory Domain Controller. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
gss_mech_free in net/sunrpc/auth_gss/gss_mech_switch.c in the rpcsec_gss_krb5 implementation in the Linux kernel through 5.6.10 lacks certain domain_release calls, leading to a memory leak. Rated medium severity (CVSS 5.5), this vulnerability is low attack complexity. No vendor patch available.
An issue was discovered in xfs_agf_verify in fs/xfs/libxfs/xfs_alloc.c in the Linux kernel through 5.6.10. Rated medium severity (CVSS 5.5), this vulnerability is low attack complexity.
An issue was found in Linux kernel before 5.5.4. Rated high severity (CVSS 7.8), this vulnerability is low attack complexity. This Out-of-bounds Write vulnerability could allow attackers to write data beyond allocated buffer boundaries leading to code execution or crashes.
A potential DoS flaw was found in the virtio-fs shared file system daemon (virtiofsd) implementation of the QEMU version >= v5.0. Rated medium severity (CVSS 6.5), this vulnerability is low attack complexity. This Allocation of Resources Without Limits vulnerability could allow attackers to exhaust system resources through uncontrolled allocation.
A use-after-free flaw was found in the way samba AD DC LDAP servers, handled 'Paged Results' control is combined with the 'ASQ' control. Rated medium severity (CVSS 5.3), this vulnerability is remotely exploitable, no authentication required. No vendor patch available.
A pivot_root race condition in fs/namespace.c in the Linux kernel 4.4.x before 4.4.221, 4.9.x before 4.9.221, 4.14.x before 4.14.178, 4.19.x before 4.19.119, and 5.x before 5.3 allows local users to. Rated medium severity (CVSS 4.7).
A ZTE product is impacted by a resource management error vulnerability. Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
On BIG-IP 15.1.0-15.1.0.1, 15.0.0-15.0.1.2, and 14.1.0-14.1.2.3, undisclosed HTTP/2 requests can lead to a denial of service when sent to a virtual server configured with the Fallback Host setting. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
On BIG-IP 15.0.0-15.1.0.1, 14.1.0-14.1.2.3, 13.1.0-13.1.3.3, 12.1.0-12.1.5.1, and 11.6.1-11.6.5.1, malformed input to the DATAGRAM::tcp iRules command within a FLOW_INIT event may lead to a denial of. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
On BIG-IP 14.1.0-14.1.2.3, undisclosed requests can lead to a denial of service (DoS) when sent to BIG-IP HTTP/2 virtual servers. 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 qemuDomainGetStatsIOThread in qemu/qemu_driver.c in libvirt 4.10.0 though 6.x before 6.1.0. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, low attack complexity. This Memory Leak vulnerability could allow attackers to exhaust available memory leading to denial of service.
In filter.c in slapd in OpenLDAP before 2.4.50, LDAP search filters with nested boolean expressions can result in denial of service (daemon crash). Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available.
Apache ATS 6.0.0 to 6.2.3, 7.0.0 to 7.1.9, and 8.0.0 to 8.0.6 is vulnerable to a HTTP/2 slow read attack. 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.
A flaw was found in all ipa versions 4.x.x through 4.8.0. Rated medium severity (CVSS 5.3), this vulnerability is remotely exploitable, no authentication required. No vendor patch available.
An integer overflow was found in QEMU 4.0.1 through 4.2.0 in the way it implemented ATI VGA emulation. Rated low severity (CVSS 3.3), this vulnerability is low attack complexity.
Huawei smartphone Lion-AL00C with versions earlier than 10.0.0.205(C00E202R7P2) have a denial of service vulnerability. Rated medium severity (CVSS 5.5), this vulnerability is no authentication required, low attack complexity. No vendor patch available.
A carefully crafted or corrupt file may trigger a System.exit in Tika's OneNote Parser. Rated medium severity (CVSS 5.5), this vulnerability is no authentication required, low attack complexity.
The IGMP component in VxWorks 6.8.3 IPNET CVE patches created in 2019 has a NULL Pointer Dereference. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
Avira Antivirus before 5.0.2003.1821 on Windows allows privilege escalation or a denial of service via abuse of a symlink. Rated high severity (CVSS 7.8), this vulnerability is low attack complexity. No vendor patch available.
IBM MQ and MQ Appliance 8.0, 9.1 LTS, and 9.1 CD could allow an authenticated user cause a denial of service due to a memory leak. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
IBM MaaS360 6.82 could allow a user with pysical access to the device to crash the application which may enable the user to access restricted applications and device settings. Rated medium severity (CVSS 4.6), this vulnerability is no authentication required, low attack complexity.
A use after free vulnerability in ip_reass() in ip_input.c of libslirp 4.2.0 and prior releases allows crafted packets to cause a denial of service. Rated medium severity (CVSS 6.5), this vulnerability is low attack complexity. Public exploit code available.
An issue was discovered in Ceph through 13.2.9. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. This NULL Pointer Dereference vulnerability could allow attackers to crash the application by dereferencing a null pointer.
Server or client applications that call the SSL_check_chain() function during or after a TLS 1.3 handshake may crash due to a NULL pointer dereference as a result of incorrect handling of the. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available.
An out-of-bounds write vulnerability was found in glibc before 2.31 when handling signal trampolines on PowerPC. Rated high severity (CVSS 7.0).
A NULL pointer dereference vulnerability in the Autodesk FBX-SDK versions 2019.0 and earlier may lead to denial of service of the application. Rated medium severity (CVSS 5.5), this vulnerability is no authentication required, low attack complexity. No vendor patch available.
An intager overflow vulnerability in the Autodesk FBX-SDK versions 2019.0 and earlier may lead to denial of service of the application. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
A use-after-free issue exists in WebKitGTK before 2.28.1 and WPE WebKit before 2.28.1 via crafted web content that allows remote attackers to execute arbitrary code or cause a denial of service. Rated high severity (CVSS 8.8), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
**VERSION NOT SUPPORTED WHEN ASSIGNED** A vulnerability could cause TCM modules to reset when under high network load in TCM v10.4.x and in system v10.3.x. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
**VERSION NOT SUPPORTED WHEN ASSIGNED** A vulnerability with the former 'password' feature could allow a denial of service attack if the user is not following documented guidelines pertaining to. 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 802.11 Generic Advertisement Service (GAS) frame processing function of Cisco Wireless LAN Controller (WLC) Software could allow an unauthenticated, remote attacker to cause 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 Control and Provisioning of Wireless Access Points (CAPWAP) protocol handler of Cisco Wireless LAN Controller (WLC) Software could allow an unauthenticated, remote attacker to. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
A vulnerability in Cisco Aironet Series Access Points Software could allow an unauthenticated, adjacent attacker to cause a denial of service (DoS) condition on an affected device. Rated medium severity (CVSS 6.5), this vulnerability is no authentication required, low attack complexity. No vendor patch available.
A vulnerability in the Constrained Application Protocol (CoAP) implementation of Cisco IoT Field Network Director could allow an unauthenticated remote attacker to cause a denial of service (DoS). Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
In a certain condition, receipt of a specific BGP UPDATE message might cause Juniper Networks Junos OS and Junos OS Evolved devices to advertise an invalid BGP UPDATE message to other peers, causing. Rated high severity (CVSS 8.6), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
Buffer overflow in Intel(R) Modular Server MFS2600KISPP Compute Module may allow an unauthenticated user to potentially enable denial of service via adjacent access. Rated medium severity (CVSS 6.5), this vulnerability is no authentication required, low attack complexity. No vendor patch available.
Race condition in the Intel(R) Driver and Support Assistant before version 20.1.5 may allow an authenticated user to potentially enable denial of service via local access. Rated medium severity (CVSS 4.7).
Improper buffer restrictions in kernel mode driver for Intel(R) PROSet/Wireless WiFi products before version 21.70 on Windows 10 may allow an unprivileged user to potentially enable denial of service. Rated medium severity (CVSS 6.5), this vulnerability is no authentication required, low attack complexity. No vendor patch available.
A denial of service vulnerability exists in Windows DNS when it fails to properly handle queries, aka 'Windows DNS Denial of Service Vulnerability'. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, low attack complexity.
A denial of service vulnerability exists when Windows improperly handles objects in memory, aka 'Windows Denial of Service Vulnerability'. Rated medium severity (CVSS 5.5), this vulnerability is low attack complexity.
Vulnerability in the Oracle VM VirtualBox product of Oracle Virtualization (component: Core). Rated high severity (CVSS 8.6), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
Vulnerability in the Oracle FLEXCUBE Core Banking product of Oracle Financial Services Applications (component: Transaction Processing). Rated medium severity (CVSS 6.3), this vulnerability is remotely exploitable, low attack complexity.
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 Application Performance Management product of Oracle Enterprise Manager (component: EM Request Monitoring). Rated medium severity (CVSS 6.0), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the MySQL Connectors product of Oracle MySQL (component: Connector/J). Rated medium severity (CVSS 5.0), this vulnerability is remotely exploitable, no authentication required.
Vulnerability in the MySQL Connectors product of Oracle MySQL (component: Connector/J). Rated low severity (CVSS 2.2), this vulnerability is remotely exploitable. No vendor patch available.
Vulnerability in the Oracle Knowledge product of Oracle Knowledge (component: Information Manager Console). Rated medium severity (CVSS 5.9), this vulnerability is remotely exploitable, no authentication required. No vendor patch available.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Parser). 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: 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: Group Replication GCS). 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: PS). 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: Group Replication Plugin). Rated medium severity (CVSS 4.4), this vulnerability is remotely exploitable.
Vulnerability in the Oracle VM VirtualBox product of Oracle Virtualization (component: Core). Rated low severity (CVSS 2.8), 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: Connection Handling). 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: Charsets). 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: Information Schema). 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: 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: Optimizer). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the PeopleSoft Enterprise PeopleTools product of Oracle PeopleSoft (component: nVision). 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: Security: Privileges). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the Java SE, Java SE Embedded product of Oracle Java SE (component: Concurrency). 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: 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: Stored Procedure). 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: Compiling). 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: Memcached). Rated medium severity (CVSS 5.9), this vulnerability is remotely exploitable, no authentication required. No vendor patch available.
Vulnerability in the Oracle GraalVM Enterprise Edition product of Oracle GraalVM (component: GraalVM Compiler). Rated high severity (CVSS 7.7), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Pluggable Auth). Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the Oracle Outside In Technology product of Oracle Fusion Middleware (component: Outside In Filters). Rated high severity (CVSS 7.3), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
Vulnerability in the Oracle Outside In Technology product of Oracle Fusion Middleware (component: Outside In Filters). Rated high severity (CVSS 7.3), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
Vulnerability in the Oracle Outside In Technology product of Oracle Fusion Middleware (component: Outside In Filters). Rated high severity (CVSS 7.3), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
Vulnerability in the Oracle Outside In Technology product of Oracle Fusion Middleware (component: Outside In Filters). Rated high severity (CVSS 7.3), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
Vulnerability in the PeopleSoft Enterprise PeopleTools product of Oracle PeopleSoft (component: Query). Rated high severity (CVSS 7.1), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
Vulnerability in the Java SE, Java SE Embedded product of Oracle Java SE (component: JSSE). Rated medium severity (CVSS 5.3), 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: DML). 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: Security: Privileges). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the PeopleSoft Enterprise PeopleTools product of Oracle PeopleSoft (component: Security). Rated high severity (CVSS 8.6), 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: Security: Privileges). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the Java SE, Java SE Embedded product of Oracle Java SE (component: Security). Rated low severity (CVSS 3.7), this vulnerability is remotely exploitable, no authentication required. No vendor patch available.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Logging). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the MySQL Cluster product of Oracle MySQL (component: Cluster: General). Rated medium severity (CVSS 6.3), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.