Coraza: jsDecode Off-by-One in Octal Escape Handling Enables WAF Bypass

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.8 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N

EPSS

• CVE-2026-104774: 0.32% estimated exploitation activity in the next 30 days; percentile 25.28 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary The t:jsDecode transformation in Coraza WAF contains an off-by-one error when parsing octal escape sequences. A backslash character was incorrectly included in the octal number buffer, causing strconv.ParseInt to fail for every octal escape sequence and return a null byte instead of the decoded value that would normally be returned. This will cause all JS-escaped payloads to be corrupted, thus leading to the bypassing of these WAF rules when WAF rules that rely on jsDecode for normalization are enabled. Therefore, a real-world attack scenario: an attacker could use JavaScript octal escape sequences (\ooo) to encode attack syntax. Although the WAF cannot decode these sequences correctly, the target backend (such as a browser or application) can parse them as expected. Details Vulnerable code: internal/transformations/jsdecode.go:64-70. This is because, when entering octal mode, the loop variable i points to the backslash character \. Before entering octal mode, the pointer…

Published by the source

8 Oct 2026, 17:45 UTC

Last modified by the source

19 Oct 2026, 21:31 UTC

Source last checked

26 Oct 2026, 15:32 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-pc5q-qfxp-ggqv

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GO-2026-6696

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-pc5q-qfxp-ggqv

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# Patch Next advisory brief: CVE-2026-104774

Advisory: Coraza: jsDecode Off-by-One in Octal Escape Handling Enables WAF Bypass
IDs: CVE-2026-104774, GHSA-pc5q-qfxp-ggqv
Record: https://patchnext.com/advisories/cve-2026-104774 (revision 3, source checked 26 Oct 2026, 15:32 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Partial vendor fix; fixed versions by package: github.com/corazawaf/coraza/v3 3.8.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/corazawaf/coraza/v3: affected >= 3.0.0, < 3.8.0; fixed in 3.8.0
- Go github.com/corazawaf/coraza: affected every version
- Go github.com/corazawaf/coraza/v2: affected every version

## Suggested inspection (read-only)
- Go github.com/corazawaf/coraza/v3: check the installed version with your package manager.
- Go github.com/corazawaf/coraza: check the installed version with your package manager.
- Go github.com/corazawaf/coraza/v2: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/corazawaf/coraza/v3, github.com/corazawaf/coraza, github.com/corazawaf/coraza/v2.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GO-2026-6696 (OSV record GO-2026-6696 lists affected ranges: Go github.com/corazawaf/coraza >=0; Go github.com/corazawaf/coraza/v2 >=0; Go github.com/corazawaf/coraza/v3 >=3.0.0 <3.8.0 (fixed))
- Verified: https://osv.dev/vulnerability/GHSA-pc5q-qfxp-ggqv (OSV record GHSA-pc5q-qfxp-ggqv lists affected ranges: Go github.com/corazawaf/coraza/v3 >=3.0.0 <3.8.0 (fixed))
- Verified: https://github.com/advisories/GHSA-pc5q-qfxp-ggqv (GitHub-reviewed advisory GHSA-pc5q-qfxp-ggqv lists affected ranges: Go github.com/corazawaf/coraza/v3 >=3.0.0 <3.8.0)

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