What is CVE-2021-29624?

CVE-2021-29624 is a medium-severity vulnerability in Fastify Fastify-Csrf, classified under Reliance on Cookies without Validation and Integrity Checking. CVSS score: 6.5/10. Published 2021-05-19.

How severe is CVE-2021-29624?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Is CVE-2021-29624 known to be exploited?

1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

CSRF in Fastify Fastify-Csrf

CVE-2021-29624

fastify-csrf is an open-source plugin helps developers protect their Fastify server against CSRF attacks. Versions of fastify-csrf prior to 3.1.0 have a "double submit" mechanism using cookies with an application deployed across multiple subdomains, e.g. "heroku"-style platform as a service. Version 3.1.0 of the fastify-csrf fixes it. the vulnerability. The user of the module would need to supply a `userInfo` when generating the CSRF token to fully implement the protection on their end. This is needed only for applications hosted on different subdomains.

Published 2021-05-19 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N.

EPSS exploit prediction

EPSS: 0.008 (55.9th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 56th percentile — 55.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.008 · newest: 0.008 · change: 0.000

Affected products

Fastify Fastify-Csrf — versions < 3.1.0

Weakness classification (CWE)

Public proof-of-concept exploits

ARPSyndicate/cvemon

References

github.com/fastify/fastify-csrf/security/advisories/GHSA-rc4q-9m69-gqp8 (Patch, Third Party Advisory)
github.com/fastify/csrf/pull/2 (Patch, Third Party Advisory)
github.com/fastify/fastify-csrf/pull/51 (Patch, Third Party Advisory)
cheatsheetseries.owasp.org/cheatsheets/Cross-Site_Request_Forgery_Prevention_Ch… (Third Party Advisory)
github.com/fastify/fastify-csrf/releases/tag/v3.1.0 (Third Party Advisory)
owasp.org/www-pdf-archive/David_Johansson-Double_Defeat_of_Double-Submit_Cookie… (Third Party Advisory)

Frequently asked questions

What is CVE-2021-29624?: CVE-2021-29624 is a medium-severity vulnerability in Fastify Fastify-Csrf, classified under Reliance on Cookies without Validation and Integrity Checking. CVSS score: 6.5/10. Published 2021-05-19.
How severe is CVE-2021-29624?: Medium severity. CVSS v3 base score is 6.5 out of 10.
Is CVE-2021-29624 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.