Authentication Bypass in rack-session (CVE-2026-39324)
Summary
Authentication bypass in rack-session (CVE-2026-39324). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 2.1.2 or later.
Original description
The description as published by the source.
Rack::Session::Cookie incorrectly handles decryption failures when configured with secrets:. If cookie decryption fails, the implementation falls back to a default decoder instead of rejecting the cookie. This allows an unauthenticated attacker to supply a crafted session cookie that is accepted as valid session data without knowledge of any configured secret.
Because this mechanism is used to load session state, an attacker can manipulate session contents and potentially gain unauthorized access.
Details
When secrets: is configured, Rack::Session::Cookie attempts to decrypt incoming session cookies using one of the configured encryptors. If all decrypt attempts fail, the implementation does not reject the cookie. Instead, it falls back to decoding the cookie using a default coder.
This fallback path processes attacker-controlled cookie data as trusted session state. The behavior is implicit and occurs even when encrypted cookies are expected.
The fallback decoder is applied automatically and does not require the application to opt into a non-encrypted session format. As a result, a client can send a specially crafted cookie value that bypasses the intended integrity protections provided by secrets:.
This issue affects both default configurations and those using alternative serializers for encrypted payloads.
Impact
Any Rack application using Rack::Session::Cookie with secrets: may be affected.
[!NOTE]
Rails applications are typically not affe…
Source: GitHub Security Advisories (Global) 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-2026-39324 has been found in rack-session.
Risk of unauthorized operations or information disclosure.
What to do: upgrade rack-session to 2.1.2 or later.
If unsure, ask your IT team or search "rack-session CVE-2026-39324" on the vendor's site.
CVE-2026-39324 (rack-session) — CWE-287
Patched: 2.1.2 — apply immediately
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.
Authentication bypass (CWE-287) exists in rack-session.
Check the vendor advisory for the affected versions of rack-session.
Severity: ?. Risk of unauthorized operations or information disclosure.
Update to 2.1.2.
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 'rack-session' . 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
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1Identify exposure identify
grep -r 'rack-session' . | 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
rack-sessionを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade rack-session to 2.1.2ステージング環境で 2.1.2 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-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
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2026-39324 ruby-rack-session
- Ubuntu UBUNTU-CVE-2026-39324 ruby-rack-session Fixed in: 2.1.1-0.1ubuntu0.1
References
- advisory nvd.nist.gov
- DSA DSA-6542-1
- package github.com
- web github.com
- web github.com
- web github.com