@fastify/secure-session vulnerable to signature verification bypass via cookie signature removal

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-117549
StatePUBLISHED
Assigneropenjs
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-11-02 11:17:30 UTC
Updated2026-11-02 17:17:38 UTC
Description@fastify/secure-session is a session plugin for Fastify that stores an encrypted session in a cookie. In versions 7.5.0 through 8.4.1, when the plugin is configured with the signed cookie option, it calls the cookie unsign routine but, when the signature check reports the value as invalid, still passes the original cookie value to the session decoder, so a session whose signature did not validate is decrypted anyway. The practical effect appears when an application supplies the cookie signing secret independently of the session encryption key and rotates only the signing secret to retire existing sessions while keeping the encryption key active, because a holder of an old session cookie can strip the now obsolete signature and keep using the session. The attacker must already possess an unexpired encrypted session cookie and needs neither secret, and cannot forge session data, extend expiry, or survive rotation of the encryption key. The issue is fixed in @fastify/secure-session 8.4.2, which no longer decodes the session when the signed cookie option is set and the signature check fails, and users should upgrade to 8.4.2 or later. As a workaround, rotate the session encryption key rather than relying on rotation of the cookie signing secret alone.

Risk And Classification

Primary CVSS: v3.1 4.2 MEDIUM from ce714d77-add3-4f53-aff5-83d477b104bb

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N

Problem Types: CWE-347 | CWE-347 CWE-347: Improper Verification of Cryptographic Signature

VersionSourceTypeScoreSeverityVector
3.1ce714d77-add3-4f53-aff5-83d477b104bbSecondary4.2MEDIUMCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N
3.1CNACVSS4.2MEDIUMCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA @fastifysecure-session @fastify/secure-session affected 7.5.0 8.4.2 semver Not specified
CNA @fastifysecure-session @fastify/secure-session unaffected 8.4.2 semver Not specified

References

ReferenceSourceLinkTags
github.com/fastify/fastify-secure-session/security/advisories/GHSA-4cgq-... ce714d77-add3-4f53-aff5-83d477b104bb github.com
cna.openjsf.org/security-advisories.html ce714d77-add3-4f53-aff5-83d477b104bb cna.openjsf.org
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: nirodhav (en)

CNA: mcollina (en)

CNA: UlisesGascon (en)

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