CVE-2026-73548
Envoy: Cross-user response poisoning via a generic (non-WebSocket) HTTP upgrade on Envoy's shared backend pool
- Published
- Updated
- Reserved
- Assigned by
- GitHub_M
Description
Envoy is an open source edge and service proxy designed for cloud-native applications. Prior to 1.36.10, 1.37.6, 1.38.4, and 1.39.1, Envoy forwards data for a configured non-WebSocket HTTP upgrade before the upstream accepts the upgrade. An unauthenticated HTTP/2 client can place a complete HTTP/1.1 request in extended CONNECT data; Envoy downgrades the request, writes the data unframed to a keep-alive HTTP/1.1 upstream, and returns the socket to the shared pool while the smuggled response remains queued. A different downstream client can then receive the attacker's response. The relevant scope boundary is that webSocket upgrades, plain CONNECT, disabled backend keep-alive, per-downstream pools, and max_requests_per_connection set to 1 are not affected by the demonstrated path. This issue is fixed in versions 1.36.10, 1.37.6, 1.38.4, and 1.39.1.
Public exploit
A reference of the record is tagged as an exploit or proof of concept: anyone can try it against an unpatched system. CISA's SSVC rates its exploitation: a proof of concept is public.
- https://github.com/envoyproxy/envoy/security/advisories/GHSA-3vhp-c83q-jqc2 (opens in a new tab)x_refsource_CONFIRMexploit
Timeline
ID reserved
By GitHub_M
- 40 days later
· 40 days later
Published
- 3 days later
· 3 days later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_MCNA (assigner) | 3.1 | High7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N |
| NVDNVD · Analyzed | 3.1 | High7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N |
- EPSS (exploitation in 30 days)
- 0.46% · top 60% of all CVEs (7 Nov 2026)
- CISA SSVC
- Exploitation: poc · Automatable: yes · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.5.
Weakness
Affected products
- affected < 1.36.10
- affected >= 1.37.0, < 1.37.6
- affected >= 1.38.0, < 1.38.4
- affected >= 1.39.0, < 1.39.1
References (9)
- https://github.com/envoyproxy/envoy/security/advisories/GHSA-3vhp-c83q-jqc2 (opens in a new tab)x_refsource_CONFIRMexploit
- https://github.com/envoyproxy/envoy/commit/309855626966cff176155c821043ed3b44671361 (opens in a new tab)x_refsource_MISC
- https://github.com/envoyproxy/envoy/commit/3c7998545a9c9fb3933a4bc1907d92f0e752bc2b (opens in a new tab)x_refsource_MISC
- https://github.com/envoyproxy/envoy/commit/4633b8cce3d15b8734eefe232e30c12b0140b91c (opens in a new tab)x_refsource_MISC
- https://github.com/envoyproxy/envoy/commit/bd6711f2617658e28dfa3df3dace6bfe3cfc0766 (opens in a new tab)x_refsource_MISC
- https://github.com/envoyproxy/envoy/releases/tag/v1.36.10 (opens in a new tab)x_refsource_MISC
- https://github.com/envoyproxy/envoy/releases/tag/v1.37.6 (opens in a new tab)x_refsource_MISC
- https://github.com/envoyproxy/envoy/releases/tag/v1.38.4 (opens in a new tab)x_refsource_MISC
- https://github.com/envoyproxy/envoy/releases/tag/v1.39.1 (opens in a new tab)x_refsource_MISC
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://trackcve.app/cve/CVE-2026-73548)Record last updated .