Paper/Archive/CVE-2026-33805

CVE-2026-33805

@fastify/reply-from @fastify/reply-from — @fastify/reply-from vulnerable to connection header abuse enabling stripping of proxy-added headers

EPSS 0.4%public exploit CVSS 9.0

critical.is priorityof 100

CVSS 9.0 (CNA)9.0 / 10 × 3027.0 Not in CISA KEV+300.0 EPSS percentile 38.3.383 × 207.7 Exploit: SSVC poc+1010.0 SSVC exploitation: poc+100.0

Description · from the CVE record

@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.

Affected

ProductAffectedFixed inSource

@fastify/reply-from< 12.6.212.6.2CNA

@fastify/http-proxy< 11.4.411.4.4CNA

Red Hat OpenShift Dev Spaces 3.27see advisory1776795511redhat-SADP

Red Hat OpenShift AI (RHOAI)see advisory–redhat-SADP

Scores by source

openjs (CNA)9.0CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:L/SI:H/SA:N

redhat-SADP (CNA)7.4CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

CISA ADPSSVCExploitation: poc · Automatable: yes · Technical impact: partial

References

exploitgithub.com/fastify/fastify-reply-from/security/advisories/GHSA-gwhp-pf74-vj37 refcna.openjsf.org/security-advisories.html refaccess.redhat.com/security/cve/CVE-2026-33805 refbugzilla.redhat.com/show_bug.cgi?id=2458651 refsecurity.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33805.json advisoryaccess.redhat.com/errata/RHSA-2026:10175