CVE-2026-33805
This allows attackers to retroactively strip proxy-added headers from upstream requests by listing them in the Connection header value.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.44%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
@fastify/reply-from v12.6.1 and earlier and @fastify/http-proxy v11.4.3 and earlier process the client's Connection header after the proxy has added its own headers via rewriteRequestHeaders. This allows attackers to retroactively strip proxy-added headers from upstream requests by listing them in the Connection header value. Any header added by the proxy for routing, access control, or security purposes can be selectively removed by a client. @fastify/http-proxy is also affected as it delegates to @fastify/reply-from. Upgrade to @fastify/reply-from v12.6.2 or @fastify/http-proxy v11.4.4 or later.
- CVSS 4.0
- 9.0 CRITICALCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:L/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M
- EPSS
- 0.44% probability · 37th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-644, CWE-444
- Affected
- fastify/fastify\/http-proxy · fastify/reply-from
- Source
- ce714d77-add3-4f53-aff5-83d477b104bb
References
- https://cna.openjsf.org/security-advisories.htmlVendor Advisory
- https://github.com/fastify/fastify-reply-from/security/advisories/GHSA-gwhp-pf74-vj37Exploit, Mitigation, Vendor Advisory
- https://access.redhat.com/errata/RHSA-2026:10175
- https://access.redhat.com/security/cve/CVE-2026-33805
- https://bugzilla.redhat.com/show_bug.cgi?id=2458651
- https://github.com/fastify/fastify-reply-from/security/advisories/GHSA-gwhp-pf74-vj37Exploit, Mitigation, Vendor Advisory
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33805.json
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.