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)
Snudown is a reddit-specific fork of the Sundown Markdown parser used by GitHub, with Python integration added. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, low attack complexity. Public exploit code available.
An issue was discovered in stb stb_image.h 1.33 through 2.27. Rated medium severity (CVSS 5.5), this vulnerability is no authentication required, low attack complexity. No vendor patch available.
IBM Flash System 900 could allow an authenticated attacker to obtain sensitive information and cause a denial of service due to a restricted shell escape vulnerability. Rated high severity (CVSS 8.1), this vulnerability is remotely exploitable, low attack complexity.
A null pointer vulnerability in Trend Micro Apex One and Worry-Free Business Security 10.0 SP1 could allow an attacker to crash the CGI program on affected installations. 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.
A vulnerability in an API of the Call Bridge feature of Cisco Meeting Server could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition. 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 web-based management interface of Cisco Integrated Management Controller (IMC) Software could allow an unauthenticated, remote attacker to cause the web-based management. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
The Proof-of-Stake (PoS) Ethereum consensus protocol through 2021-10-19 allows an adversary to cause a denial of service (long-range consensus chain reorganizations), even when this adversary has. Rated critical severity (CVSS 9.1), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
The Proof-of-Stake (PoS) Ethereum consensus protocol through 2021-10-19 allows an adversary to leverage network delay to cause a denial of service (indefinite stalling of consensus decisions). Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
The Proof-of-Stake (PoS) Ethereum consensus protocol through 2021-10-19 allows an adversary to cause a denial of service (delayed consensus decisions), and also increase the profits of individual. Rated critical severity (CVSS 9.1), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
modern-async is an open source JavaScript tooling library for asynchronous operations using async/await and promises. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available.
In Camaleon CMS, versions 2.0.1 to 2.6.0 are vulnerable to an Uncaught Exception. Rated medium severity (CVSS 4.3), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the Oracle Outside In Technology product of Oracle Fusion Middleware (component: Outside In Filters). Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
Vulnerability in the Oracle Outside In Technology product of Oracle Fusion Middleware (component: Outside In Filters). Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
Vulnerability in the Oracle Outside In Technology product of Oracle Fusion Middleware (component: Outside In Filters). Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
Vulnerability in the Oracle Outside In Technology product of Oracle Fusion Middleware (component: Outside In Filters). Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
Vulnerability in the Oracle Outside In Technology product of Oracle Fusion Middleware (component: Outside In Filters). Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
Vulnerability in the Oracle Outside In Technology product of Oracle Fusion Middleware (component: Outside In Filters). Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
Vulnerability in the Oracle Outside In Technology product of Oracle Fusion Middleware (component: Outside In Filters). Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
Vulnerability in the Essbase Administration Services product of Oracle Essbase (component: EAS Console). Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
Vulnerability in the Oracle Secure Global Desktop product of Oracle Virtualization (component: Client). Rated medium severity (CVSS 4.6), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the Oracle Secure Global Desktop product of Oracle Virtualization (component: Server). Rated medium severity (CVSS 5.4), this vulnerability is remotely exploitable, low attack complexity.
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. 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: 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: 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: 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: 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: 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: Logging). 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: Server: Data Dictionary). Rated medium severity (CVSS 4.4), this vulnerability is low attack complexity. No vendor patch available.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: GIS). 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: 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: Encryption). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
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 Cluster product of Oracle MySQL (component: Cluster: General). Rated low severity (CVSS 1.8). No vendor patch available.
Vulnerability in the MySQL Cluster product of Oracle MySQL (component: Cluster: General). 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: Optimizer). Rated medium severity (CVSS 5.5), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the Oracle Sales Offline product of Oracle E-Business Suite (component: Offline Template). Rated medium severity (CVSS 4.3), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Optimizer). Rated high severity (CVSS 7.1), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Group Replication Plugin). Rated medium severity (CVSS 5.3), this vulnerability is remotely exploitable.
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.
Vulnerability in the MySQL Server product of Oracle MySQL (component: InnoDB). Rated medium severity (CVSS 5.5), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Options). Rated medium severity (CVSS 5.0), this vulnerability is remotely exploitable.
Vulnerability in the MySQL Client product of Oracle MySQL (component: C API). 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: Error Handling). 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: DML). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the Oracle Solaris product of Oracle Systems (component: Device drivers). Rated medium severity (CVSS 6.0), this vulnerability is low attack complexity.
Vulnerability in the Java SE, Oracle GraalVM Enterprise Edition product of Oracle Java SE (component: Hotspot). Rated low severity (CVSS 3.1), this vulnerability is remotely exploitable, no authentication required.
Vulnerability in the Java SE, Oracle GraalVM Enterprise Edition 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 Cluster product of Oracle MySQL (component: Cluster: ndbcluster/plugin DDL). Rated medium severity (CVSS 4.3), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Windows). Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
Vulnerability in the Oracle Applications Manager product of Oracle E-Business Suite (component: View Reports). Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the Java SE, Oracle GraalVM Enterprise Edition product of Oracle Java SE (component: JSSE). 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: Optimizer). 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: Optimizer). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the Oracle Outside In Technology product of Oracle Fusion Middleware (component: Outside In Filters). Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
Vulnerability in the Oracle Outside In Technology product of Oracle Fusion Middleware (component: Outside In Filters). Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
Vulnerability in the Oracle Outside In Technology product of Oracle Fusion Middleware (component: Outside In Filters). Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
Vulnerability in the Java SE, Oracle GraalVM Enterprise Edition product of Oracle Java SE (component: JSSE). Rated medium severity (CVSS 5.3), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
Vulnerability in the Java SE, Oracle GraalVM Enterprise Edition product of Oracle Java SE (component: Utility). Rated medium severity (CVSS 5.3), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
Vulnerability in the Java SE, Oracle GraalVM Enterprise Edition product of Oracle Java SE (component: Swing). Rated medium severity (CVSS 5.3), 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.
Vulnerability in the Core RDBMS component of Oracle Database Server. Rated medium severity (CVSS 4.3), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the Core RDBMS component of Oracle Database Server. Rated medium severity (CVSS 4.3), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the Java SE, Oracle GraalVM Enterprise Edition product of Oracle Java SE (component: Swing). Rated medium severity (CVSS 5.3), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
Vulnerability in the RDBMS Security component of Oracle Database Server. Rated medium severity (CVSS 5.5), this vulnerability is remotely exploitable, low attack complexity.
Vulnerability in the Oracle Solaris product of Oracle Systems (component: Utility). Rated low severity (CVSS 3.9), this vulnerability is 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 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 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 5.5), this vulnerability is low attack complexity. No vendor patch available.
Vulnerability in the Oracle Solaris product of Oracle Systems (component: Filesystem). Rated medium severity (CVSS 6.5), this vulnerability is 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 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: 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: DML). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the Oracle Applications Framework product of Oracle E-Business Suite (component: Session Management). Rated medium severity (CVSS 5.3), this vulnerability is remotely exploitable, no authentication required, 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 Communications Interactive Session Recorder product of Oracle Communications (component: Provision API). Rated high severity (CVSS 8.3), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
Vulnerability in the Oracle Communications Session Border Controller product of Oracle Communications (component: Routing). Rated medium severity (CVSS 4.9), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
Vulnerability in the Oracle LogMiner component of Oracle Database Server. Rated medium severity (CVSS 6.7), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.