{"id":"CVE-2026-49753","aliases":["GHSA-mjqx-c6f6-7rc2"],"title":"mint: Content-Length header accepts non-RFC \"+\" sign prefix","summary":"mint: Content-Length header accepts non-RFC \"+\" sign prefix","severity":"medium","cwe":["CWE-444"],"vendor":"mint","product":"mint","ecosystem":"erlang","affected":["mint < 1.9.0"],"patched":["mint 1.9.0"],"published":"2026-07-09","updated":"2026-07-09","source":"GHSA","sourceUrl":"https://github.com/advisories/GHSA-mjqx-c6f6-7rc2","references":[{"url":"https://github.com/elixir-mint/mint/security/advisories/GHSA-mjqx-c6f6-7rc2"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-49753"},{"url":"https://github.com/elixir-mint/mint/commit/47e48027480228e4e32a0b4df39db497b4804921"},{"url":"https://cna.erlef.org/cves/CVE-2026-49753.html"},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-49753"},{"url":"https://github.com/advisories/GHSA-mjqx-c6f6-7rc2"}],"tags":["ghsa","erlang"],"epss":0.00301,"epssPercentile":0.22979,"ingestedAt":"2026-07-09T23:53:27.240Z","slug":"CVE-2026-49753","body":"## Overview\n\n### Summary\n\nMint's HTTP/1 client accepts `Content-Length` header values with a leading `+` sign (e.g. `+0`, `+123`), which RFC 7230 forbids (`Content-Length = 1*DIGIT`). On a connection shared with a strict fronting proxy or load balancer, this parser disagreement is a response-smuggling primitive: the proxy frames the body one way, Mint frames it another, and bytes meant for one response leak into the next consumer's response stream.\n\n### Details\n\n`'Elixir.Mint.HTTP1.Parse':content_length_header/1` in `lib/mint/http1/parse.ex` parses the header value with `Integer.parse/1`. By design, `Integer.parse/1` accepts an optional `+` or `-` sign prefix. The `length >= 0` guard rules out negatives, but inputs such as `\"+0\"`, `\"+123\"`, or `\"+1\"` pass through and are returned as valid lengths.\n\nA strict proxy or load balancer rejects or reframes `Content-Length: +0\\r\\n`, while Mint silently treats it as `0`. When Mint reuses the socket (keep-alive, pipelining, or any pooled connection) and the connection is shared with a proxy that frames the same bytes differently, trailing bytes the proxy attributes to response N are attributed by Mint to response N+1. Across trust boundaries (shared pools, multi-tenant fronting) this enables response smuggling.\n\n### PoC\n\n1. Stand up a raw TCP server that returns `HTTP/1.1 200 OK\\r\\nContent-Length: +0\\r\\nConnection: keep-alive\\r\\n\\r\\n<smuggled bytes>`.\n2. Connect a Mint HTTP/1 client to the server and issue a request.\n3. Observe that Mint reports the response as status 200 with `Content-Length: \"+0\"` and an empty body, leaving the smuggled bytes sitting in the socket buffer for the next response.\n\n### Impact\n\nResponse-smuggling / request-response desync primitive in Mint's HTTP/1 client parser. Anyone using Mint (directly or via Finch, Tesla's Mint adapter, Req, etc.) to talk through a shared or pooled connection where a fronting proxy enforces RFC 7230 strictly while Mint does not is exposed. The attacker is the response producer (a malicious or compromised upstream, or anything that can inject bytes into a shared origin response); exploitation into a cross-request data leak additionally requires the deployment to share a Mint connection across trust boundaries.\n\n## Resources\n\n* Introduction commit: https://github.com/elixir-mint/mint/commit/65e0e86d799a6d3b08e4372fccdd9747535e0dd6\n* Patch commit: https://github.com/elixir-mint/mint/commit/47e48027480228e4e32a0b4df39db497b4804921\n\n## Affected packages\n\n- `mint < 1.9.0`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `mint 1.9.0`","depth":"sunlit","depthScore":28,"depthScoreParts":{"impact":27.5,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}