Inefficient regular expression complexity in Ajv - CVE-2025-69873

Detailed vulnerability description

The vulnerability allows a local user to perform a denial of service (DoS) attack.

The vulnerability exists due to the pattern keyword accepts runtime data via JSON Pointer syntax ($data reference), which is passed directly to the JavaScript RegExp() constructor without validation, when the $data option is enabled. A local user can can inject a malicious regex pattern (e.g., "^(a|a)*$") 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.

How to mitigate CVE-2025-69873

Sources

• https://github.com/EthanKim88/ethan-cve-disclosures/blob/main/CVE-2025-69873-ajv-ReDoS.md
• https://github.com/advisories/GHSA-2g4f-4pwh-qvx6
• https://github.com/ajv-validator/ajv/pull/2588
• https://github.com/ajv-validator/ajv/pull/2590
• https://github.com/ajv-validator/ajv/releases/tag/v6.14.0
• https://github.com/github/advisory-database/pull/6991