CVE-2025-57821 is a medium-severity (CVSS 4.2) Open Redirect vulnerability in google_sign_in. A fix is available for google_sign_in — see the affected versions and patch details below.
Basecamp's Google Sign-In for Rails allowed redirects to a malformed URL
Exploitation Status
No confirmed exploitation observed yet
- 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 CVE-2025-57821.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
google_sign_inReal-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
Summary
It is possible to craft a malformed URL that passes the "same origin" check, resulting in the user being redirected to another origin.
Details
The google_sign_in gem persists an optional URL for redirection after authentication. If this URL is malformed, it's possible for the user to be redirected to another origin after authentication, possibly resulting in exposure of authentication information such as the token.
Normally the value of this URL is only written and read by the library. If applications are configured to store session information in a database, there is no known vector to exploit this vulnerability. However, applications may be configured to store this information in a session cookie, in which case it may be chained with a session cookie attack to inject a crafted URL.
Impact
Rails applications configured to store the flash information in a session cookie may be vulnerable, if this can be chained with an attack that allows injection of arbitrary data into the session cookie.
Workarounds
If you are unable to upgrade this library, then you may mitigate the chained attack by explicitly setting SameSite=Lax or SameSite=Strict on the application session cookie.
Credits
This issue was responsibly reported by Hackerone user muntrive.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | google_sign_in | all versions | 1.3.0bundle update google_sign_in --conservative |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for google_sign_in, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update google_sign_in to 1.3.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-57821 is resolved across your whole dependency graph.
Workarounds
Stop reflecting attacker-controlled destinations: resolve every redirect target against an allowlist of paths or hosts you own, prefer a server-side key over a full URL in the request, and reject absolute URLs entirely where the flow only ever needs a relative one.
Frequently Asked Questions
Is CVE-2025-57821 in your dependencies?
Find it across RubyGems, including transitive dependencies.