CVE-2025-69873 in ajv
Summary
by MITRE • 02/11/2026
ajv (Another JSON Schema Validator) before 8.18.0 is vulnerable to Regular Expression Denial of Service (ReDoS) when the $data option is enabled. The pattern keyword accepts runtime data via JSON Pointer syntax ($data reference), which is passed directly to the JavaScript RegExp() constructor without validation. An attacker can inject a malicious regex pattern (e.g., "^(a|a)*$") combined with crafted input to cause catastrophic backtracking. A 31-character payload causes approximately 44 seconds of CPU blocking, with each additional character doubling execution time. This enables complete denial of service with a single HTTP request against any API using ajv with $data: true for dynamic schema validation. This issue is also fixed in version 6.14.0.
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Analysis
by VulDB Data Team • 06/10/2026
The vulnerability identified as CVE-2025-69873 affects the ajv JSON schema validator library version 8.17.0 and earlier, presenting a critical Regular Expression Denial of Service (ReDoS) threat when the $data option is enabled. This flaw stems from the library's handling of runtime data through JSON Pointer syntax, where the pattern keyword accepts dynamic input that gets directly passed to JavaScript's RegExp() constructor without proper sanitization or validation. The vulnerability operates under CWE-400, specifically targeting improper input validation of regular expressions, making it a prime example of how dynamic regex patterns can be exploited for denial of service attacks. The issue manifests when an attacker crafts malicious regex patterns that trigger catastrophic backtracking in the JavaScript engine's regex processor, creating exponential execution time growth that can effectively freeze system resources.
The operational impact of this vulnerability is severe and directly translates to complete service disruption for applications relying on ajv with the $data feature enabled. When an attacker submits a specially crafted payload containing a malicious regex pattern such as "^(a|a)*$", the system undergoes catastrophic backtracking that results in prolonged CPU blocking. The mathematical progression of this attack shows that a 31-character payload can consume approximately 44 seconds of processing time, with each additional character causing the execution time to double exponentially. This exponential growth means that even relatively small payloads can cause substantial system degradation, potentially leading to complete denial of service conditions that can affect entire APIs or web services. The attack requires only a single HTTP request to inflict maximum damage, making it particularly dangerous for high-traffic applications.
Security practitioners should recognize this vulnerability as part of the broader ATT&CK framework's T1499.004 technique, which covers network denial of service through resource exhaustion. The attack vector specifically aligns with T1210, where adversaries exploit weaknesses in input validation mechanisms to consume system resources. Organizations using ajv with the $data option should immediately implement mitigation strategies including upgrading to version 8.18.0 or later, where the fix has been implemented to validate and sanitize regex patterns before passing them to the RegExp constructor. Additionally, implementing rate limiting and input validation at multiple layers of the application architecture can help prevent exploitation. The fix in version 6.14.0 demonstrates the importance of proper regex validation, which should include bounds checking, maximum length restrictions, and pattern sanitization to prevent attackers from crafting malicious inputs that can cause exponential execution time growth. Organizations should also consider implementing monitoring and alerting for unusual CPU usage patterns that might indicate ReDoS attacks.