{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-39803", "assignerOrgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "state": "PUBLISHED", "assignerShortName": "EEF", "dateReserved": "2026-04-07T12:28:54.916Z", "datePublished": "2026-05-13T13:36:09.648Z", "dateUpdated": "2026-05-27T15:40:37.538Z" }, "containers": { "cna": { "affected": [ { "collectionURL": "https://repo.hex.pm", "cpes": [ "cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*" ], "defaultStatus": "unaffected", "modules": [ "'Elixir.Bandit.HTTP1.Socket'" ], "packageName": "bandit", "packageURL": "pkg:hex/bandit", "product": "bandit", "programFiles": [ "lib/bandit/http1/socket.ex" ], "programRoutines": [ { "name": "'Elixir.Bandit.HTTP1.Socket':read_data/2" }, { "name": "'Elixir.Bandit.HTTP1.Socket':do_read_chunked_data!/5" } ], "repo": "https://github.com/mtrudel/bandit", "vendor": "mtrudel", "versions": [ { "lessThan": "1.11.1", "status": "affected", "version": "1.4.0", "versionType": "semver" } ] }, { "collectionURL": "https://github.com", "cpes": [ "cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*" ], "defaultStatus": "unaffected", "modules": [ "'Elixir.Bandit.HTTP1.Socket'" ], "packageName": "mtrudel/bandit", "packageURL": "pkg:github/mtrudel/bandit", "product": "bandit", "programFiles": [ "lib/bandit/http1/socket.ex" ], "programRoutines": [ { "name": "'Elixir.Bandit.HTTP1.Socket':read_data/2" }, { "name": "'Elixir.Bandit.HTTP1.Socket':do_read_chunked_data!/5" } ], "repo": "https://github.com/mtrudel/bandit", "vendor": "mtrudel", "versions": [ { "lessThan": "ae3520dfdbfab115c638f8c7f6f6b805db34e1ab", "status": "affected", "version": "903e209a521bc216b9f9065c01ae9a0cac2d5a10", "versionType": "git" } ] } ], "cpeApplicability": [ { "nodes": [ { "cpeMatch": [ { "criteria": "cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*", "versionEndExcluding": "1.11.1", "versionStartIncluding": "1.4.0", "vulnerable": true } ], "negate": false, "operator": "OR" } ], "operator": "AND" } ], "credits": [ { "lang": "en", "type": "finder", "value": "Peter Ullrich" }, { "lang": "en", "type": "remediation developer", "value": "Mat Trudel" }, { "lang": "en", "type": "analyst", "value": "Jonatan Männchen / EEF" } ], "descriptions": [ { "lang": "en", "supportingMedia": [ { "base64": false, "type": "text/html", "value": "Allocation of Resources Without Limits or Throttling vulnerability in mtrudel bandit allows unauthenticated remote denial of service via memory exhaustion.

The chunked clause of 'Elixir.Bandit.HTTP1.Socket':read_data/2 in lib/bandit/http1/socket.ex ignores the caller-supplied :length option when reading HTTP/1 chunked request bodies. Instead of capping the accumulated body at the configured limit (e.g. Plug.Parsers' default 8 MB), do_read_chunked_data!/5 buffers every received chunk into an iolist unconditionally and materializes the entire body as a single binary. The function always returns {:ok, body, ...}, so callers cannot interpose a 413 response.

Because Plug.Parsers runs before routing and authentication in the standard Phoenix endpoint, an unauthenticated attacker needs no valid route or credentials. Sending a single Transfer-Encoding: chunked POST request with an arbitrarily large body to any path causes the BEAM process to exhaust available memory and be terminated by the OS OOM killer.

The content-length path in the same function correctly enforces the limit and is not affected.

This issue affects bandit: from 1.4.0 before 1.11.1.

" } ], "value": "Allocation of Resources Without Limits or Throttling vulnerability in mtrudel bandit allows unauthenticated remote denial of service via memory exhaustion.\n\nThe chunked clause of 'Elixir.Bandit.HTTP1.Socket':read_data/2 in lib/bandit/http1/socket.ex ignores the caller-supplied :length option when reading HTTP/1 chunked request bodies. Instead of capping the accumulated body at the configured limit (e.g. Plug.Parsers' default 8 MB), do_read_chunked_data!/5 buffers every received chunk into an iolist unconditionally and materializes the entire body as a single binary. The function always returns {:ok, body, ...}, so callers cannot interpose a 413 response.\n\nBecause Plug.Parsers runs before routing and authentication in the standard Phoenix endpoint, an unauthenticated attacker needs no valid route or credentials. Sending a single Transfer-Encoding: chunked POST request with an arbitrarily large body to any path causes the BEAM process to exhaust available memory and be terminated by the OS OOM killer.\n\nThe content-length path in the same function correctly enforces the limit and is not affected.\n\nThis issue affects bandit: from 1.4.0 before 1.11.1." } ], "impacts": [ { "capecId": "CAPEC-130", "descriptions": [ { "lang": "en", "value": "CAPEC-130 Excessive Allocation" } ] } ], "metrics": [ { "cvssV4_0": { "attackComplexity": "LOW", "attackRequirements": "NONE", "attackVector": "NETWORK", "baseScore": 8.7, "baseSeverity": "HIGH", "privilegesRequired": "NONE", "subAvailabilityImpact": "NONE", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "userInteraction": "NONE", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N", "version": "4.0", "vulnAvailabilityImpact": "HIGH", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE" }, "format": "CVSS", "scenarios": [ { "lang": "en", "value": "GENERAL" } ] } ], "problemTypes": [ { "descriptions": [ { "cweId": "CWE-770", "description": "CWE-770 Allocation of Resources Without Limits or Throttling", "lang": "en", "type": "CWE" } ] } ], "providerMetadata": { "orgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "shortName": "EEF", "dateUpdated": "2026-05-27T15:40:37.538Z" }, "references": [ { "tags": [ "vendor-advisory", "related" ], "url": "https://github.com/mtrudel/bandit/security/advisories/GHSA-9q9q-324x-93r2" }, { "tags": [ "related" ], "url": "https://cna.erlef.org/cves/CVE-2026-39803.html" }, { "tags": [ "related" ], "url": "https://osv.dev/vulnerability/EEF-CVE-2026-39803" }, { "tags": [ "patch" ], "url": "https://github.com/mtrudel/bandit/commit/ae3520dfdbfab115c638f8c7f6f6b805db34e1ab" } ], "source": { "discovery": "EXTERNAL" }, "title": "HTTP/1 chunked body reader ignores length cap in bandit", "x_generator": { "engine": "cvelib 1.8.0" } }, "adp": [ { "references": [ { "url": "https://github.com/mtrudel/bandit/security/advisories/GHSA-9q9q-324x-93r2", "tags": [ "exploit" ] } ], "metrics": [ { "other": { "type": "ssvc", "content": { "timestamp": "2026-05-13T14:41:58.440838Z", "id": "CVE-2026-39803", "options": [ { "Exploitation": "poc" }, { "Automatable": "yes" }, { "Technical Impact": "partial" } ], "role": "CISA Coordinator", "version": "2.0.3" } } } ], "title": "CISA ADP Vulnrichment", "providerMetadata": { "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-05-13T14:43:25.158Z" } } ] } }