Vulnerability in cowlib (CVE-2026-43969)
Summary
Vulnerability in cowlib (CVE-2026-43969). Risk of unauthorized operations or information disclosure.
Original description
The description as published by the source.
Summary
Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability in ninenines cowlib allows HTTP request splitting and cookie smuggling via unvalidated cookie name and value fields.
cow_cookie:cookie/1 in cowlib builds a client-side Cookie: request header from a list of name-value pairs without validating either field. An attacker who controls the cookie names or values passed to this function can inject ;, ,, CR, LF, or TAB characters into the serialized header. This enables two classes of attack: cookie smuggling within a single header (e.g. injecting ; admin=1 to introduce a phantom cookie that the receiving server treats as authentic) and HTTP request header splitting (injecting CRLF to append arbitrary headers or smuggle a complete second request against a shared upstream proxy). The decoder side (parse_cookie_name/1, parse_cookie_value/1) and setcookie/3 already validate and reject these characters; the encoder alone is missing the check.
This issue affects cowlib: from 2.9.0 before 2.21.0.
Workarounds
Validate inputs into cow_cookie:cookie/1 to only include valid cookie name and value characters as defined in RFC 6265 Section 4.1.1 before passing them to the function.
Configurations
The application must pass attacker-controlled bytes as cookie names or values to cow_cookie:cookie/1. Applications that construct cookie lists exclusively from trusted, application-controlled values are not affected.
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-43969 has been found in cowlib.
Risk of unauthorized operations or information disclosure. CVSS score: 3.2/10.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "cowlib CVE-2026-43969" on the vendor's site.
CVE-2026-43969 (cowlib) — CWE-93 / CVSS v3 3.2
Attack vector: local / unauthenticated / no user interaction
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-93) exists in cowlib.
Check the vendor advisory for the affected versions of cowlib.
Severity: Low (CVSS 3.2/10). Risk of unauthorized operations or information disclosure.
Update to the patched release per vendor advisory.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'cowlib' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'cowlib' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
cowlibを grep し、稼働しているサービス・バージョンを把握する。 -
2Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory osv.dev
- advisory nvd.nist.gov
- package hex.pm
- package github.com
- patch github.com
- patch github.com
- web cna.erlef.org
- web github.com
- web github.com