fastify vulnerable to Denial of Service via unhandled exception on HTTP/2 trailer responses
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- High
- Impact type
- Denial of service
- Confidentiality · integrity · availability
- None · None · High
- Fix status
- Partial Red Hat: 3 without a fix
Attack profile from CVSS 3.1 · CNA. Fix status from CNA, GitHub and Red Hat. Impact type from CWE-248.
Summary
fastify is a fast and low-overhead web framework for Node.js. In versions before 5.12.5, when a route registers a response trailer via reply.trailer() and is served over HTTP/2, fastify unconditionally sets the Transfer-Encoding: chunked header, which is forbidden on HTTP/2, so Node.js throws while serializing the response headers. The exception is not caught and becomes an uncaughtException, so a single unauthenticated HTTP/2 request to any route that uses trailers crashes the server process and drops all in-flight requests, and it can be repeated on every restart. The issue is fixed in fastify 5.12.5, and users should upgrade to 5.12.5 or later. As a workaround, avoid registering response trailers with reply.trailer() on routes served over HTTP/2 until upgrading.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| fastify | fastify | before 5.12.5 | 5.12.5 | Patch available | CNA |
| — | fastify (npm) | before 5.12.5 | 5.12.5 | Patch available | GHSA-4mh8-r7rc-xpvc |
- fastify Vendorfastify Affected before 5.12.5 Fixed in 5.12.5 Patch available CNA
- fastify (npm) Vendor— Affected before 5.12.5 Fixed in 5.12.5 Patch available GHSA-4mh8-r7rc-xpvc
Remediation
- Fix · CNA fastify (fastify) Fixed in 5.12.5
- Fix · GHSA-4mh8-r7rc-xpvc fastify (npm) Fixed in 5.12.5 Advisory →
Vendor assessments
Red Hat
Red Hat rating: Moderate. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Enterprise Linux AI (RHEL AI) 3 | Affected | No fix yet: Fix deferred |
| Red Hat OpenShift AI (RHOAI) | Affected | No fix yet: Fix deferred |
| Red Hat OpenShift Dev Spaces | Affected | No fix yet: Fix deferred |
Timeline
- 2026-10-02 Threatist record created from CVE-2026-92081
- 2026-10-03 Alias added: GHSA-4mh8-r7rc-xpvc
References
Other 6
- https://github.com/fastify/fastify/security/advisories/GHSA-4mh8-r7rc-xpvc
- https://cna.openjsf.org/security-advisories.html
- https://github.com/fastify/fastify/issues/6574
- https://github.com/fastify/fastify/commit/ad06a4c3fe8a944a904f38068249b18b8f552e90
- https://github.com/fastify/fastify
- https://github.com/fastify/fastify/releases/tag/v5.12.5
More fastify vulnerabilities
- TI-2026-26180 @fastify/express vulnerable to middleware authentication bypass via URL normalization… CVSS 4.0CRITICAL 9.1
- TI-2026-26179 @fastify/express vulnerable to middleware path doubling causing authentication bypass in child plugin scopes CVSS 3.1CRITICAL 9.1
- TI-2026-26177 @fastify/reply-from vulnerable to connection header abuse enabling stripping of proxy-added headers CVSS 4.0CRITICAL 9.0
- TI-2026-05498 @fastify/middie vulnerable to middleware authentication bypass in child plugin scopes CVSS 3.1CRITICAL 9.1
- TI-2023-15307 Cross-site request forgery in npm @fastify/oauth2 CVSS 3.1HIGH 8.8
- TI-2022-18664 Denial of service in Fastify via Content-Type header CVSS 3.1HIGH 7.5
Sources
- CVE-2026-92081 · CVE Program
- CVE-2026-92081 · NVD
- FIRST EPSS
- GHSA-4mh8-r7rc-xpvc · GitHub Advisory Database · CC BY 4.0
- CVE-2026-92081 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences