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Medium, CVSS 5.3amended

Bypass of CSRF protection in the presence of predictable userInfo

CVE-2023-27495GHSA-qrgf-9gpc-vrxw

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (@fastify/csrf-protection 6.3.0, 4.1.0), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
5.3 · CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N
EPSS
  • CVE-2023-27495: 0.33% estimated exploitation activity in the next 30 days; percentile 26.36 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

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…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-qrgf-9gpc-vrxw

  2. Revision 1 · created ·

    Published from osv record GHSA-qrgf-9gpc-vrxw

Agent brief

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# Patch Next advisory brief: CVE-2023-27495

Advisory: Bypass of CSRF protection in the presence of predictable userInfo
IDs: CVE-2023-27495, GHSA-qrgf-9gpc-vrxw
Record: https://patchnext.com/advisories/cve-2023-27495 (revision 2, source checked 26 Oct 2026, 12:27 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @fastify/csrf-protection 6.3.0, 4.1.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @fastify/csrf-protection: affected < 4.1.0; >= 5.0.0, < 6.3.0; fixed in 6.3.0, 4.1.0

## Suggested inspection (read-only)
- `npm ls @fastify/csrf-protection --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @fastify/csrf-protection.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-qrgf-9gpc-vrxw (OSV record GHSA-qrgf-9gpc-vrxw lists affected ranges: npm @fastify/csrf-protection >=0 =5.0.0 <6.3.0 (fixed))
- Verified: https://github.com/advisories/GHSA-qrgf-9gpc-vrxw (GitHub-reviewed advisory GHSA-qrgf-9gpc-vrxw lists affected ranges: npm @fastify/csrf-protection >=0 =5.0.0 <6.3.0)

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