Exploitation requires a deployment topology in which an RFC-strict HTTP/1 intermediary (proxy, load balancer, or WAF) sits between the Mint client and the attacker-influenced origin, and HTTP/1 connections between the client and the intermediary are reused across requests (keep-alive with connection pooling). Mint clients that talk directly to an origin without an intermediary, or that do not reuse connections, are not exploitable for response-queue poisoning even if the vulnerable parsing behavior is present.
" }, { "base64": false, "type": "text/markdown", "value": "Exploitation requires a deployment topology in which an RFC-strict HTTP/1 intermediary (proxy, load balancer, or WAF) sits between the Mint client and the attacker-influenced origin, and HTTP/1 connections between the client and the intermediary are reused across requests (keep-alive with connection pooling). Mint clients that talk directly to an origin without an intermediary, or that do not reuse connections, are not exploitable for response-queue poisoning even if the vulnerable parsing behavior is present." } ], "value": "Exploitation requires a deployment topology in which an RFC-strict HTTP/1 intermediary (proxy, load balancer, or WAF) sits between the Mint client and the attacker-influenced origin, and HTTP/1 connections between the client and the intermediary are reused across requests (keep-alive with connection pooling). Mint clients that talk directly to an origin without an intermediary, or that do not reuse connections, are not exploitable for response-queue poisoning even if the vulnerable parsing behavior is present." } ], "cpeApplicability": [ { "nodes": [ { "cpeMatch": [ { "criteria": "cpe:2.3:a:elixir-mint:mint:*:*:*:*:*:*:*:*", "versionEndExcluding": "1.10.1", "versionStartIncluding": "0.1.0", "vulnerable": true } ], "negate": false, "operator": "OR" } ], "operator": "AND" } ], "credits": [ { "lang": "en", "type": "finder", "value": "Eurico Nicacio" }, { "lang": "en", "type": "reporter", "value": "Eurico Nicacio" }, { "lang": "en", "type": "remediation developer", "value": "Eric Meadows-Jönsson" }, { "lang": "en", "type": "remediation reviewer", "value": "Andrea Leopardi" } ], "dateAssigned": "2026-09-19T15:55:00.000Z", "descriptions": [ { "lang": "en", "supportingMedia": [ { "base64": false, "type": "text/html", "value": "Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') vulnerability in elixir-mint mint allows a malicious HTTP/1 server to desynchronize a strict intermediary and the Mint client on a pooled connection, enabling response-queue poisoning against subsequent requests that share the connection.
\nMint.HTTP1.Parse.chunk_size/1 in lib/mint/http1/parse.ex stops at the first non-hexadecimal byte of a chunked response's chunk-size line and returns the remainder unexamined. Mint.HTTP1.decode_body/5 in lib/mint/http1.ex then discards every byte up to the CRLF with Parse.ignore_until_crlf/1, so the accepted grammar is a run of hex digits followed by arbitrary bytes, where RFC 9112 permits only a ;-introduced chunk extension. Lines such as 5ZZZZZ and 5 9 are accepted as chunk size 5, and 0ZZZZ is accepted as the terminating chunk that ends the message body. An RFC-strict intermediary rejects such a line while Mint accepts it, so the two disagree on chunk boundaries and on where the response ends.
This issue affects mint: from 0.1.0 before 1.10.1.
" }, { "base64": false, "type": "text/markdown", "value": "Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') vulnerability in elixir-mint mint allows a malicious HTTP/1 server to desynchronize a strict intermediary and the Mint client on a pooled connection, enabling response-queue poisoning against subsequent requests that share the connection.\n\n`Mint.HTTP1.Parse.chunk_size/1` in `lib/mint/http1/parse.ex` stops at the first non-hexadecimal byte of a chunked response's chunk-size line and returns the remainder unexamined. `Mint.HTTP1.decode_body/5` in `lib/mint/http1.ex` then discards every byte up to the CRLF with `Parse.ignore_until_crlf/1`, so the accepted grammar is a run of hex digits followed by arbitrary bytes, where RFC 9112 permits only a `;`-introduced chunk extension. Lines such as `5ZZZZZ` and `5 9` are accepted as chunk size 5, and `0ZZZZ` is accepted as the terminating chunk that ends the message body. An RFC-strict intermediary rejects such a line while Mint accepts it, so the two disagree on chunk boundaries and on where the response ends.\n\nThis issue affects mint: from 0.1.0 before 1.10.1." } ], "value": "Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') vulnerability in elixir-mint mint allows a malicious HTTP/1 server to desynchronize a strict intermediary and the Mint client on a pooled connection, enabling response-queue poisoning against subsequent requests that share the connection.\n\nMint.HTTP1.Parse.chunk_size/1 in lib/mint/http1/parse.ex stops at the first non-hexadecimal byte of a chunked response's chunk-size line and returns the remainder unexamined. Mint.HTTP1.decode_body/5 in lib/mint/http1.ex then discards every byte up to the CRLF with Parse.ignore_until_crlf/1, so the accepted grammar is a run of hex digits followed by arbitrary bytes, where RFC 9112 permits only a ;-introduced chunk extension. Lines such as 5ZZZZZ and 5 9 are accepted as chunk size 5, and 0ZZZZ is accepted as the terminating chunk that ends the message body. An RFC-strict intermediary rejects such a line while Mint accepts it, so the two disagree on chunk boundaries and on where the response ends.\n\nThis issue affects mint: from 0.1.0 before 1.10.1." } ], "impacts": [ { "capecId": "CAPEC-273", "descriptions": [ { "lang": "en", "supportingMedia": [ { "base64": false, "type": "text/html", "value": "A malicious or attacker-influenced HTTP/1 origin behind an RFC-strict intermediary can make the intermediary and the Mint client disagree on chunk boundaries and on where the response body ends. On a pooled keep-alive connection that disagreement lets bytes from one response be attributed to the next, poisoning the responses returned to unrelated requests that share the connection.
" }, { "base64": false, "type": "text/markdown", "value": "A malicious or attacker-influenced HTTP/1 origin behind an RFC-strict intermediary can make the intermediary and the Mint client disagree on chunk boundaries and on where the response body ends. On a pooled keep-alive connection that disagreement lets bytes from one response be attributed to the next, poisoning the responses returned to unrelated requests that share the connection." } ], "value": "A malicious or attacker-influenced HTTP/1 origin behind an RFC-strict intermediary can make the intermediary and the Mint client disagree on chunk boundaries and on where the response body ends. On a pooled keep-alive connection that disagreement lets bytes from one response be attributed to the next, poisoning the responses returned to unrelated requests that share the connection." } ] } ], "metrics": [ { "cvssV4_0": { "Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "Safety": "NOT_DEFINED", "attackComplexity": "LOW", "attackRequirements": "PRESENT", "attackVector": "NETWORK", "baseScore": 6.3, "baseSeverity": "MEDIUM", "privilegesRequired": "NONE", "providerUrgency": "NOT_DEFINED", "subAvailabilityImpact": "NONE", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "userInteraction": "NONE", "valueDensity": "NOT_DEFINED", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N", "version": "4.0", "vulnAvailabilityImpact": "NONE", "vulnConfidentialityImpact": "LOW", "vulnIntegrityImpact": "LOW", "vulnerabilityResponseEffort": "NOT_DEFINED" }, "format": "CVSS", "scenarios": [ { "lang": "en", "value": "GENERAL" } ] } ], "problemTypes": [ { "descriptions": [ { "cweId": "CWE-444", "description": "CWE-444 Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')", "lang": "en", "type": "CWE" } ] } ], "providerMetadata": { "orgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "shortName": "EEF", "dateUpdated": "2026-09-19T17:00:31.648Z" }, "references": [ { "name": "GitHub Advisory", "tags": [ "related", "vendor-advisory" ], "url": "https://github.com/elixir-mint/mint/security/advisories/GHSA-rj5m-69wp-cxq9" }, { "name": "EEF CNA record for CVE-2026-82672", "tags": [ "related" ], "url": "https://cna.erlef.org/cves/CVE-2026-82672.html" }, { "name": "OSV record EEF-CVE-2026-82672", "tags": [ "related" ], "url": "https://osv.dev/vulnerability/EEF-CVE-2026-82672" }, { "name": "Introducing commit 6008958 in elixir-mint/mint", "tags": [ "related" ], "url": "https://github.com/elixir-mint/mint/commit/60089586ec7adc9fddb09f69a2f5919ba9ac7f33" }, { "name": "Fix commit c823778 in elixir-mint/mint", "tags": [ "patch" ], "url": "https://github.com/elixir-mint/mint/commit/c82377838dc6e275ef40bafa664fbcdf50270c60" } ], "source": { "discovery": "EXTERNAL" }, "title": "Unvalidated chunk-size line tail in Mint HTTP/1 client enables response smuggling against strict intermediaries on pooled connections", "x_proofOfConcept": [ { "lang": "en", "supportingMedia": [ { "base64": false, "type": "text/html", "value": "HTTP/1.1 200 OK response with transfer-encoding: chunked and controls the chunk-size line byte for byte.Mint.HTTP1 (mint 1.10.0 from Hex), send a request and stream the response.+5, Z5 and 00000000000000005 are refused with :invalid_chunk_size, confirming the build carries the earlier chunk-size fixes.5 and 5;name=value are accepted with body hello.5ZZZZZ, 5 anything at all, 5<TAB>foo, 5 9 and 5}~! are each accepted as chunk size 5 with body hello.0ZZZZ and 0 9 in place of the final 0 chunk are accepted and end the body.Content-Length: +5, Content-Length: 5ZZZ and Content-Length: 5 9 are refused with :invalid_content_length_header in the same run.The reporter ran this on Elixir 1.18 / OTP 27 and Elixir 1.18.4 / OTP 28 with identical results.
" }, { "base64": false, "type": "text/markdown", "value": "1. Start a loopback TCP server that serves one `HTTP/1.1 200 OK` response with `transfer-encoding: chunked` and controls the chunk-size line byte for byte.\n2. Connect with `Mint.HTTP1` (mint 1.10.0 from Hex), send a request and stream the response.\n3. Positive controls: chunk-size lines `+5`, `Z5` and `00000000000000005` are refused with `:invalid_chunk_size`, confirming the build carries the earlier chunk-size fixes.\n4. Baseline: `5` and `5;name=value` are accepted with body `hello`.\n5. Finding: `5ZZZZZ`, `5 anything at all`, `51. Chunk-size parsing. Mint.HTTP1.Parse.chunk_size/1 in lib/mint/http1/parse.ex folds leading hexadecimal digits into an accumulator through parse_hex_prefix/3 and, on the first byte that is not a hex digit, returns {:ok, size, rest} with rest unexamined. The sign and digit-count checks added by earlier fixes constrain only the digits.
2. Tail skipping. The caller, Mint.HTTP1.decode_body/5 in lib/mint/http1.ex, hands rest to Parse.ignore_until_crlf/1, which advances over any byte until it finds CRLF. Nothing between the last hex digit and the CRLF is validated, so the accepted grammar is 1*HEXDIG *OCTET CRLF, where RFC 9112 section 7.1 allows only an optional ;-introduced chunk-ext. The same tolerance applies to the terminating zero-length chunk, which is the token that ends the message body.
3. Parser disagreement. The sibling Content-Length parser, Mint.HTTP1.Parse.content_length_header/1, trims trailing whitespace and requires the whole remaining value to be digits, rejecting anything else. An RFC-strict intermediary that rejects or reframes a chunk-size line with a non-extension tail, on a connection where Mint accepts it, yields a framing disagreement about chunk length and, through the terminating chunk, about where the message ends.