EUVD-2026-39975
GHSA-xrr7-82jr-v58x
Severity by source
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Network-accessible, no auth required, but AC:H because backend must misparse the ambiguous message; scope changes as cross-client response poisoning affects other users.
Primary rating from Vendor (VulnCheck).
CVSS VectorVendor: VulnCheck
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Lifecycle Timeline
3DescriptionCVE.org
nghttp2's nghttpx proxy through 1.69.0 forwards an HTTP/1.1 Upgrade request that also carries a Content-Length header and body onto reusable keep-alive backend connections, re-adding the Upgrade and Connection headers while passing Content-Length verbatim. A backend that resolves the resulting ambiguous message in the attacker's favor enables HTTP request/response smuggling and cross-client response-queue poisoning.
AnalysisAI
HTTP request/response smuggling in nghttpx (the reverse proxy component of nghttp2 through 1.69.0) allows unauthenticated remote attackers to poison shared backend keep-alive connections by crafting an HTTP/1.1 Upgrade request that simultaneously carries a Content-Length header and body. When nghttpx forwards this ambiguous message to a backend and re-adds Connection and Upgrade headers while passing Content-Length verbatim, a backend that resolves the parsing ambiguity in the attacker's favor treats the body as a separate, attacker-controlled HTTP request - enabling cross-client response-queue poisoning. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires that nghttpx is operating as a reverse proxy (not the HTTP/2 client or server library modes) and that backend connections are pooled and reused via HTTP keep-alive - the default configuration for nghttpx in proxy mode. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 4.0 score of 6.3 (Medium) reflects the real-world complexity of exploitation: AC:H correctly captures that the attack succeeds only when the downstream backend resolves the parsing ambiguity in the attacker's favor - not all backends are vulnerable to this specific interaction. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An unauthenticated attacker sends a crafted HTTP/1.1 request to nghttpx bearing both an Upgrade header and a Content-Length body whose bytes spell out a malicious HTTP request (e.g., a GET to an admin endpoint). nghttpx forwards the ambiguous message onto an existing keep-alive connection to a backend that interprets the Content-Length body as a second, pipelined HTTP request. … |
| Remediation | The primary fix is to update nghttp2 to a version that includes upstream commit ab28105c4a0197da24f8bfc414bc116055249e1e (https://github.com/nghttp2/nghttp2/commit/ab28105c4a0197da24f8bfc414bc116055249e1e); a specific tagged release version is not confirmed in the available data - verify with the nghttp2 project release page. … Detailed patch versions, workarounds, and compensating controls in full report. |
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Same weakness CWE-444 – HTTP Request/Response Smuggling
View allSame technique Information Disclosure
View allVendor StatusVendor
Debian
Bug #1140917| Release | Status | Fixed Version | Urgency |
|---|---|---|---|
| bullseye | vulnerable | 1.43.0-1+deb11u1 | - |
| bullseye (security) | vulnerable | 1.43.0-1+deb11u3 | - |
| bookworm | vulnerable | 1.52.0-1+deb12u2 | - |
| bookworm (security) | vulnerable | 1.52.0-1+deb12u3 | - |
| trixie | vulnerable | 1.64.0-1.1 | - |
| trixie (security) | vulnerable | 1.64.0-1.1+deb13u1 | - |
| forky, sid | vulnerable | 1.69.0-1 | - |
| (unstable) | fixed | (unfixed) | - |
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External POC / Exploit Code
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