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VulnerabilityPublished

CVE-2026-120215: @fastify/cors · Uncaught Exception

Affects @fastify/corsSource CVE Database V5

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Not known to be exploited · CVSS 3.7 Low : upgrade to 11.4.0 when convenient.

Data as of 2 Nov 2026, 11:12 UTC

CVSS 3.1 base score
3.7Low
How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none
CVSS scores by source
CNA (openjs)CVSS 3.13.7
Patch
Available – fixed in 11.4.0
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 2 Nov 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2 Nov 2026.

What to do

Upgrade @fastify/cors to 11.4.0.

Affected software

ProductAffectedFixed in
@fastify/cors@fastify/corsAffected
  • >=8.2.0 <11.4.0
Fixed in
  • 11.4.0
npm@fastify/corspkg:npm/@fastify/corsOther threatsAffected
  • >=8.2.0 <11.4.0
Fixed in
  • 11.4.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Upgrade to @fastify/cors version 11.4.0 or later, where the onSend hook option is no longer accepted and registration fails with a clear error instead of crashing at runtime. As a workaround, avoid using the onSend hook by using other hooks such as the default onRequest, or set the preflight option to false to prevent the crash.

Description

@fastify/cors versions 8.2.0 through 11.3.x have a vulnerability where using the non-default onSend hook option causes the application to crash on CORS preflight OPTIONS requests. This happens because the plugin calls reply.send inside the onSend hook, triggering an uncaught ERR_HTTP_HEADERS_SENT error that can terminate the Node.js process. The issue is fixed in version 11.4.0, which disallows onSend as a hook option and fails registration with a clear error instead of crashing at runtime.

References

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