How severe is CVE-2023-27495?

CVE-2023-27495 has a CVSS score of 5.3/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2023-27495?

CVE-2023-27495 affects the following packages: @fastify/csrf-protection (npm), @fastify/csrf-protection (npm). Ecosystems affected: npm.

How do I fix CVE-2023-27495?

Update @fastify/csrf-protection to 4.1.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-27495 is resolved across your whole dependency graph.

How do I detect CVE-2023-27495 in my npm dependencies?

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

How do I mitigate CVE-2023-27495 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-2023-27495 actively exploited in the wild?

No public exploit code has been indexed for CVE-2023-27495 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-2023-27495?

CVE-2023-27495 has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 26th 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-2023-27495?

CVE-2023-27495 is classified as Cross-Site Request Forgery (CSRF) (CWE-352). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2023-27495 published, and has it been updated?

CVE-2023-27495 was published on April 20, 2023 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

MEDIUM severity

CVE-2023-27495 — @fastify/csrf-protection

MEDIUMFix: fastify/csrf-protection@be3e576

CVE-2023-27495 is a medium-severity (CVSS 5.3) Cross-Site Request Forgery (CSRF) vulnerability in @fastify/csrf-protection. A fix is available for @fastify/csrf-protection — see the affected versions and patch details below.

Bypass of CSRF protection in the presence of predictable userInfo in @fastify/csrf-protection

Also known asGHSA-qrgf-9gpc-vrxw

Published

Apr 20, 2023

Updated

Oct 28, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Oct 31, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2023-27495.

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs26th percentile — riskier than 26% 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

2 pkgs 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.

23other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

@fastify/csrf-protectionnpm

188Kdownloads / week

Description

The CSRF protection enforced by the @fastify/csrf-protection library in combination with @fastify/cookie can be bypassed from network and same-site attackers under certain conditions.

@fastify/csrf-protection supports an optional userInfo parameter that binds the CSRF token to the user. This parameter has been introduced to prevent cookie-tossing attacks as a fix for CVE-2021-29624. Whenever userInfo parameter is missing, or its value can be predicted for the target user account, network and same-site attackers can 1. fixate a _csrf cookie in the victim's browser, and 2. forge CSRF tokens that are valid for the victim's session. This allows attackers to bypass the CSRF protection mechanism.

As a fix, @fastify/csrf-protection starting from version 6.3.0 (and v4.1.0) includes a server-defined secret hmacKey that cryptographically binds the CSRF token to the value of the _csrf cookie and the userInfo parameter, making tokens non-spoofable by attackers. This protection is effective as long as the userInfo parameter is unique for each user.

Patches

This is patched in version 6.3.0 and v4.1.0.

Workarounds

As a workaround, developers can use a random, non-predictable userInfo parameter for each user.

Credits

Pedro Adão (@pedromigueladao), Instituto Superior Técnico, University of Lisbon
Marco Squarcina (@lavish), Security & Privacy Research Unit, TU Wien

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`@fastify/csrf-protection`	all versions	4.1.0`npm install @fastify/csrf-protection@4.1.0`
📦npm	`@fastify/csrf-protection`	≥ 5.0.0&&< 6.3.0	6.3.0`npm install @fastify/csrf-protection@6.3.0`

Affected Products

1 product · 2 configurations

Application

csrf-protectionfastify

≥ 5.0.0 && < 6.3.0

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-protection, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update @fastify/csrf-protection to 4.1.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-27495 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

## Description The [CSRF](https://owasp.org/www-community/attacks/csrf) protection enforced by the `@fastify/csrf-protection` library in combination with `@fastify/cookie` can be bypassed from network and same-site attackers under certain conditions. `@fastify/csrf-protection` supports an optional `userInfo` parameter that binds the CSRF token to the user. This parameter has been introduced to prevent cookie-tossing attacks as a fix for [CVE-2021-29624](https://www.cvedetails.com/cve/CVE-2021-29624). Whenever `userInfo` parameter is missing, or its value can be predicted for the target user a