{"id":"CVE-2026-73051","aliases":["GHSA-xhj4-vrgc-hr34"],"url":"https://o3.security/vulnerability/CVE-2026-73051","summary":"actix-http before 3.12.1 HTTP Request Smuggling via CL.TE","details":"A vulnerability in `actix-http`'s HTTP/1.1 request parser allows an unauthenticated remote client to smuggle requests in deployments where a front-end HTTP intermediary and the Actix backend disagree about whether `Content-Length` or `Transfer-Encoding: chunked` defines the request body length.\n\n## Severity\n\n**Medium**.\nThis is an HTTP request smuggling vulnerability that can be triggered over the network without application-level credentials. Exploitation requires a specific proxy topology: an upstream proxy, WAF, load balancer, or similar intermediary must use `Content-Length` framing while forwarding the conflicting `Transfer-Encoding: chunked` request to an Actix backend over a reused HTTP/1.1 connection.\n\n## Affected Versions\n\n- `actix-http`: versions up to and including **3.12.0**\n\n## Description\n\nHTTP/1.1 requests that contain both `Content-Length` and `Transfer-Encoding: chunked` are ambiguous and must be rejected by recipients to avoid request smuggling.\n\nAffected versions of `actix-http` accepted a request with a syntactically valid `Content-Length` header and `Transfer-Encoding: chunked` on the same HTTP/1.1 message. The parser then selected chunked decoding instead of rejecting the conflicting framing signals.\n\nIn a CL.TE proxy topology, an intermediary may treat bytes after the declared `Content-Length` body as part of the first request, while the Actix backend stops at the terminating chunk marker and parses the remaining bytes on the backend connection as a second HTTP request. This creates a backend-side request desynchronization primitive.\n\nThe issue is limited to HTTP/1.1 request parsing.\n\n## Impact\n\n**HTTP request smuggling**\n\n* **Attack Vector:** Network, unauthenticated.\n* **Effect:** Backend request desynchronization with low integrity impact to requests processed by the vulnerable Actix service.\n* **Scope:** Actix services using affected `actix-http` versions behind an HTTP/1.1 intermediary that forwards ambiguous `Content-Length` plus `Transfer-Encoding: chunked` requests and reuses backend connections.\n\nNo direct confidentiality, availability, or subsequent-system impact is scored for this advisory.\n\n## Fixed Versions\n\nThis issue is fixed in **actix-http 3.12.1**.\n\nThe fix rejects HTTP/1.1 requests that contain both `Content-Length` and `Transfer-Encoding: chunked` instead of choosing one framing interpretation.\n\n## Mitigation\n\nUsers should upgrade to **actix-http 3.12.1** or later.\n\nApplications that depend on `actix-http` through `actix-web`, `awc`, or another Actix crate should ensure dependency resolution selects `actix-http` 3.12.1 or later. For example:\n\n```bash\ncargo update -p actix-http\n```\n\nIf an immediate upgrade is not possible, configure all upstream HTTP intermediaries to reject HTTP/1.1 requests that contain both `Content-Length` and `Transfer-Encoding`, and avoid forwarding ambiguous request framing to Actix backends.\n## Credits\n\nActix thanks [mufeedvh](https://github.com/mufeedvh) who disclosed this issue through coordinated disclosure.","published":"2026-08-14T11:35:45.780Z","modified":"2026-10-20T12:02:19.235585987Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"crates.io","name":"actix-http","fixedVersion":"3.12.1"}],"fix":null,"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/73xxx/CVE-2026-73051.json"},{"type":"ADVISORY","url":"https://github.com/actix/actix-web/security/advisories/GHSA-xhj4-vrgc-hr34"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-73051"},{"type":"ADVISORY","url":"https://www.vulncheck.com/advisories/actix-http-before-http-request-smuggling-via-cl-te"},{"type":"PACKAGE","url":"https://github.com/actix/actix-web"},{"type":"WEB","url":"https://github.com/actix/actix-web/releases/tag/http-v3.12.1"},{"type":"WEB","url":"https://www.rfc-editor.org/rfc/rfc9112.html#name-message-body-length"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-20T12:02:19.235585987Z"}}