How severe is CVE-2024-35220?

CVE-2024-35220 has a CVSS score of 7.4/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2024-35220?

CVE-2024-35220 affects the following packages: @fastify/session (npm). Ecosystems affected: npm.

How do I fix CVE-2024-35220?

Update @fastify/session to 10.9.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2024-35220 is resolved across your whole dependency graph.

How do I detect CVE-2024-35220 in my npm dependencies?

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

How do I mitigate CVE-2024-35220 if there is no patch (or I can't update yet)?

Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Is CVE-2024-35220 actively exploited in the wild?

No public exploit code has been indexed for CVE-2024-35220 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-2024-35220?

CVE-2024-35220 has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 39th 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-2024-35220?

CVE-2024-35220 is classified as CWE-613 (CWE-613). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2024-35220 published, and has it been updated?

CVE-2024-35220 was published on May 21, 2024 and was last updated on October 28, 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

HIGH severity

CVE-2024-35220 — @fastify/session

HIGHFix: fastify/session@0495ce5

CVE-2024-35220 is a high-severity (CVSS 7.4) CWE-613 vulnerability in @fastify/session. A fix is available for @fastify/session — see the affected versions and patch details below.

@fastify/session reuses destroyed session cookie

Also known asGHSA-pj27-2xvp-4qxg

Published

May 21, 2024

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 4, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.

Exploitation and automatability from CISA’s SSVC triage for CVE-2024-35220.

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs39th percentile — riskier than 39% of all scored CVEsHighest risk

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

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.

46other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

@fastify/sessionnpm

298Kdownloads / week

Description

Impact

When restoring the cookie from the session store, the expires field is overriden if the maxAge field was set. This means a cookie is never correctly detected as expired and thus expired sessions are not destroyed.

Patches

Updating to v10.9.0 will solve this.

Workarounds

None

References

Publicly reported at: https://github.com/fastify/session/issues/251

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`@fastify/session`	all versions	10.9.0`npm install @fastify/session@10.9.0`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @fastify/session, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update @fastify/session to 10.9.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2024-35220 is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Frequently Asked Questions

### Impact When restoring the cookie from the session store, the `expires` field is overriden if the `maxAge` field was set. This means a cookie is never correctly detected as expired and thus expired sessions are not destroyed. ### Patches Updating to v10.9.0 will solve this. ### Workarounds None ### References Publicly reported at: https://github.com/fastify/session/issues/251