CVE-2026-104774: OWASP Coraza WAF: jsDecode Off-by-One in Octal Escape Handling Enables WAF Bypass

Vulnerability summary

CVE-2026-104774 is a medium (CVSS 5.8) Improper Encoding or Decoding of Data vulnerability in corazawaf coraza. EPSS estimates a 0.32% chance of exploitation in the next 30 days, higher than 25.2% of scored vulnerabilities.

Timeline

1. 12-10-2026
   PublishedVulnerability first disclosed.
2. 13-10-2026
   Last modifiedVulnerability information updated.

Description

OWASP Coraza WAF is a golang modsecurity compatible web application firewall library. From 3.0.0 until 3.8.0, the t:jsDecode transformation in internal/transformations/js_decode.go:64-70 includes the backslash in the octal buffer, causing ParseInt to fail and return a null byte. The flaw is triggered when a rule relies on t:jsDecode and the request contains JavaScript octal escape sequences. An unauthenticated attacker can encode attack syntax with JavaScript octal escapes so the backend decodes the intended bytes while Coraza rules using t:jsDecode inspect corrupted null-byte output. The mismatch can bypass WAF rules and expose the protected application to attacks such as cross-site scripting or SQL injection. This issue is fixed in version 3.8.0.

• CWE-172Improper Encoding or Decoding of DataThe product does not properly encode or decode data, resulting in unexpected values that are not equivalent to the original data.
• CWE-193Off-by-one ErrorA product calculates or uses an incorrect maximum or minimum value that is 1 more, or 1 less, than the correct value.
• CWE-693Protection Mechanism FailureThe product does not use or incorrectly uses a protection mechanism that provides sufficient defense against directed attacks against the product.