Formbricks missing JWT signature verification

published 2025-09-26 13 mo ago modified 2026-10-19 20 d ago also EUVD-2025-31394

cvss: 9.4; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 9.5%; EPSS 9.5% chance of exploitation in 30 days, percentile 95%
public exploits: 0; none known

Formbricks is an open source qualtrics alternative. Prior to version 4.0.1, Formbricks is missing JWT signature verification. This vulnerability stems from a token validation routine that only decodes JWTs (jwt.decode) without verifying their signatures. Both the email verification token login path and the password reset server action use the same validator, which does not check the token’s signature, expiration, issuer, or audience. If an attacker learns the victim’s actual user.id, they can craft an arbitrary JWT with an alg: "none" header and use it to authenticate and reset the victim’s password. This issue has been patched in version 4.0.1.

Patch / fix

links 2

github.com/formbricks/formbricks@eb1349f commit
github.com/formbricks/formbricks#6596 pull request

CISA SSVC

Exploitation: Proof of concept is public
Automatable: yes
Technical impact: partial
Assessed: 13 mo ago (2025-09-29)

Exploit prediction

9.46% chance of exploitation in the next 30 days, higher than 95% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	9.4	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L

Affected products

formbricks formbricks

Classification

Weakness

CWE-347 Improper Verification of Cryptographic Signature
CWE-345 Insufficient Verification of Data Authenticity
CWE-287 Improper Authentication

References

Sources

CVE List CVE-2025-59934
NVD CVE-2025-59934

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary