How severe is CVE-2021-29624?

CVE-2021-29624 has a CVSS score of 6.5/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2021-29624?

CVE-2021-29624 affects the following packages: fastify-csrf (npm). Ecosystems affected: npm.

How do I fix CVE-2021-29624?

Update fastify-csrf to 3.1.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-29624 is resolved across your whole dependency graph.

How do I detect CVE-2021-29624 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for fastify-csrf, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-29624 if there is no patch (or I can't update yet)?

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.

Is CVE-2021-29624 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-29624 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2021-29624?

CVE-2021-29624 has an EPSS (Exploit Prediction Scoring System) score of 0.8%, placing it in the 57th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-29624?

CVE-2021-29624 is classified as CWE-565 (CWE-565), Cross-Site Request Forgery (CSRF) (CWE-352). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-29624 published, and has it been updated?

CVE-2021-29624 was published on May 19, 2021 and was last updated on October 20, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦

📦 npm

Not in CISA KEV

MEDIUM severity

CVE-2021-29624 — fastify-csrf

MEDIUMFix: fastify/csrf#2

CVE-2021-29624 is a medium-severity (CVSS 6.5) CWE-565 vulnerability in fastify-csrf. A fix is available for fastify-csrf — see the affected versions and patch details below.

Lack of protection against cookie tossing attacks in fastify-csrf

Also known asGHSA-rc4q-9m69-gqp8

Published

May 19, 2021

Updated

Oct 20, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 23, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

0.8%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs57th percentile — riskier than 57% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2021-29624 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 395,249 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

8other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

fastify-csrfnpm

1Kdownloads / week

Description

Impact

Users that used fastify-csrf with the "double submit" mechanism using cookies with an application deployed across multiple subdomains, e.g. "heroku"-style platform as a service.

Patches

Version 3.1.0 of the fastify-csrf fixes it. See https://github.com/fastify/fastify-csrf/pull/51 and https://github.com/fastify/csrf/pull/2.

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.

Workarounds

None available.

References

Credits

This vulnerability was found by Xhelal Likaj [email protected].

For more information

If you have any questions or comments about this advisory:

Open an issue in fastify-csrf
Email us at [email protected]

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`fastify-csrf`	all versions	3.1.0`npm install fastify-csrf@3.1.0`

Affected Products

1 product · 1 configurations

Application

fastify-csrffastify

< 3.1.0

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for fastify-csrf, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update fastify-csrf to 3.1.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-29624 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.

Frequently Asked Questions

### Impact Users that used fastify-csrf with the "double submit" mechanism using cookies with an application deployed across multiple subdomains, e.g. "heroku"-style platform as a service. ### Patches Version 3.1.0 of the fastify-csrf fixes it. See https://github.com/fastify/fastify-csrf/pull/51 and https://github.com/fastify/csrf/pull/2. 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. ### Workarounds None available. ### Reference