GHSA-33qg-7wpp-89cq — rack-session
GHSA-33qg-7wpp-89cq is a Improper Authentication vulnerability in rack-session. A fix is available for rack-session — see the affected versions and patch details below.
Rack::Session::Cookie secrets: decrypt failure fallback enables secretless session forgery and Marshal deserialization
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-33qg-7wpp-89cq.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
rack-sessionReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.
Description
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 affected — Rails uses
ActionDispatch::Session::CookieStore, which is a separate implementation backed byActiveSupport::MessageEncryptorand does not share the vulnerable code path.
An unauthenticated attacker can supply a crafted session cookie that is accepted as valid session data. This can lead to authentication bypass or privilege escalation in applications that rely on session values for identity or authorization decisions.
Depending on application behavior and available runtime components, processing of untrusted session data may also expose additional risks.
Mitigation
- Update to a patched version of
rack-sessionthat rejects cookies when decryption fails under thesecrets:configuration.- After updating, rotate session secrets to invalidate existing session cookies, since attacker-supplied session data may have been accepted and re-issued prior to the fix.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | rack-session | ≥ 2.0.0&&< 2.1.2 | 2.1.2bundle update rack-session --conservative |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for rack-session, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update rack-session to 2.1.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-33qg-7wpp-89cq is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-33qg-7wpp-89cq can be triaged on real exposure rather than presence alone.
Tailored to GHSA-33qg-7wpp-89cq. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-33qg-7wpp-89cq in your dependencies?
O3 Security finds GHSA-33qg-7wpp-89cq across RubyGems dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.