Open Redirect in Basecamp Google Sign In

CVE-2025-57821

Basecamp's Google Sign-In adds Google sign-in to Rails applications. Prior to version 1.3.0, it is possible to craft a malformed URL that passes the "same origin" check, resulting in the user being redirected to another origin. 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. This issue has been patched in version 1.3.0. If upgrading is not possible at this time, a way to mitigate the chained attack can be done by explicitly setting SameSite=Lax or SameSite=Strict on the application session cookie.

Vulnerability class: Open Redirect

Published · last modified .

CVSS v3 metric

CVSS v3 base score 4.2 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.002 (13.7th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 14th percentile — 13.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2025-57821: held from 0.002 to 0.002.

EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: 0.000

Affected products

Weakness classification (CWE)

Public proof-of-concept exploits

References

Frequently asked questions

What is CVE-2025-57821?
CVE-2025-57821 is a medium-severity vulnerability in Basecamp Google Sign In, classified under URL Redirection to Untrusted Site (Open Redirect). CVSS score: 4.2/10. Published 2025-08-27.
How severe is CVE-2025-57821?
Medium severity. CVSS v3 base score is 4.2 out of 10.
Is CVE-2025-57821 known to be exploited?
1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.