CVE-2026-117499 (CVSS 3.7)

Description

@fastify/session is a session plugin for Fastify. In all releases before 11.1.6, with the default rolling session behavior, a request that restored a session before a logout could save its own copy after another request had completed the session destroy call, recreating the destroyed session identifier with its authenticated data. An attacker who already holds a victim's valid signed session cookie and keeps a request in flight across the logout can replay that cookie to restore the session after it was meant to be revoked, without any cookie theft or signature forgery. The issue is fixed in @fastify/session 11.1.6, which adds a per session generation marker and a conditional store write so a session restored before a logout or regeneration cannot recreate or overwrite the current entry, and users should upgrade to 11.1.6 or later. There is no workaround, and custom session stores must implement the new conditional write.

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CVSS v3.1 Score

3.7

LOW

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

EPSS — Exploit Prediction

0.0009

Probability of exploitation

0.01%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-362 CWE-362

CWE-613 CWE-613

References

Other References

https://cna.openjsf.org/security-advisories.html https://github.com/fastify/session/security/advisories/GHSA-2hw7-jxfh-4rm3

Frequently Asked Questions

What is CVE-2026-117499? +

@fastify/session is a session plugin for Fastify. In all releases before 11.1.6, with the default rolling session behavior, a request that restored a session before a logout could save its own copy after another request had completed the session destroy call, recreating the destroyed session identifier with its authenticated data. An attacker who already holds a victim's valid signed session cookie and keeps a request in flight across the logout can replay that cookie to restore the session after it was meant to be revoked, without any cookie theft or signature forgery. The issue is fixed in @fastify/session 11.1.6, which adds a per session generation marker and a conditional store write so a session restored before a logout or regeneration cannot recreate or overwrite the current entry, and users should upgrade to 11.1.6 or later. There is no workaround, and custom session stores must implement the new conditional write. It has a CVSS v3.1 base score of 3.7 (LOW).

How severe is CVE-2026-117499? +

CVE-2026-117499 has a CVSS v3.1 score of 3.7 out of 10, rated LOW. This is a low-severity vulnerability with limited impact. The EPSS score is 0.0009, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-117499? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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