Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability in mtrudel bandit allows an unauthenticated remote attacker to smuggle CR, LF, or NUL characters into application-visible request headers via HTTP/2. Bandit.HTTP2.Stream.read_headers/1 validates pseudo-header placement and uniqueness, header-name casing, connection-specific headers, the te value, and content-length, but never checks field values. Because HPACK carries arbitrary octets, a HEADERS block whose field values contain \\r, \\n, or \\0 decodes without error and the values land in conn.req_headers unchanged. The HTTP/1 path already rejects the same octets; HTTP/2 did not.
Bandit itself is not a sink for the injected bytes: its own logging uses fixed strings or inspect, and HTTP/2 response headers are HPACK-encoded and separately rejected by Plug's put_resp_header, so response splitting is not reachable through this path. The risk is entirely in how a downstream application consumes header values, such as appending one verbatim to a plain-text log or concatenating it into an upstream request. A related gap bundled in the same fix: only :method, :scheme, and :path were checked for at most one occurrence; a duplicate :authority pseudo-header was accepted, with the first instance silently winning as conn.host while a conflicting value remained visible to the application.
This issue affects bandit: from 1.4.0 before 1.12.5.
"},{"base64":false,"type":"text/markdown","value":"Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability in mtrudel bandit allows an unauthenticated remote attacker to smuggle CR, LF, or NUL characters into application-visible request headers via HTTP/2. `Bandit.HTTP2.Stream.read_headers/1` validates pseudo-header placement and uniqueness, header-name casing, connection-specific headers, the `te` value, and `content-length`, but never checks field *values*. Because HPACK carries arbitrary octets, a HEADERS block whose field values contain `\\r`, `\\n`, or `\\0` decodes without error and the values land in `conn.req_headers` unchanged. The HTTP/1 path already rejects the same octets; HTTP/2 did not.\n\nBandit itself is not a sink for the injected bytes: its own logging uses fixed strings or `inspect`, and HTTP/2 response headers are HPACK-encoded and separately rejected by Plug's `put_resp_header`, so response splitting is not reachable through this path. The risk is entirely in how a downstream application consumes header values, such as appending one verbatim to a plain-text log or concatenating it into an upstream request. A related gap bundled in the same fix: only `:method`, `:scheme`, and `:path` were checked for at most one occurrence; a duplicate `:authority` pseudo-header was accepted, with the first instance silently winning as `conn.host` while a conflicting value remained visible to the application.\n\nThis issue affects bandit: from 1.4.0 before 1.12.5."}],"value":"Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability in mtrudel bandit allows an unauthenticated remote attacker to smuggle CR, LF, or NUL characters into application-visible request headers via HTTP/2. Bandit.HTTP2.Stream.read_headers/1 validates pseudo-header placement and uniqueness, header-name casing, connection-specific headers, the te value, and content-length, but never checks field values. Because HPACK carries arbitrary octets, a HEADERS block whose field values contain \\r, \\n, or \\0 decodes without error and the values land in conn.req_headers unchanged. The HTTP/1 path already rejects the same octets; HTTP/2 did not.\n\nBandit itself is not a sink for the injected bytes: its own logging uses fixed strings or inspect, and HTTP/2 response headers are HPACK-encoded and separately rejected by Plug's put_resp_header, so response splitting is not reachable through this path. The risk is entirely in how a downstream application consumes header values, such as appending one verbatim to a plain-text log or concatenating it into an upstream request. A related gap bundled in the same fix: only :method, :scheme, and :path were checked for at most one occurrence; a duplicate :authority pseudo-header was accepted, with the first instance silently winning as conn.host while a conflicting value remained visible to the application.\n\nThis issue affects bandit: from 1.4.0 before 1.12.5."}],"impacts":[{"capecId":"CAPEC-81","descriptions":[{"lang":"en","value":"CAPEC-81 Web Server Logs Tampering"}]}],"metrics":[{"cvssV4_0":{"Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","Safety":"NOT_DEFINED","attackComplexity":"LOW","attackRequirements":"NONE","attackVector":"NETWORK","baseScore":6.9,"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:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N","version":"4.0","vulnAvailabilityImpact":"NONE","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"LOW","vulnerabilityResponseEffort":"NOT_DEFINED"},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-93","description":"CWE-93 Improper Neutralization of CRLF Sequences ('CRLF Injection')","lang":"en","type":"CWE"}]}],"providerMetadata":{"dateUpdated":"2026-08-20T21:11:27.523Z","orgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","shortName":"EEF"},"references":[{"tags":["vendor-advisory","related"],"url":"https://github.com/mtrudel/bandit/security/advisories/GHSA-x3gh-xhj4-3vq8"},{"tags":["related"],"url":"https://cna.erlef.org/cves/CVE-2026-75484.html"},{"tags":["related"],"url":"https://osv.dev/vulnerability/EEF-CVE-2026-75484"},{"tags":["patch"],"url":"https://github.com/mtrudel/bandit/commit/d38cf046c9a3cae4d0f88001c2ceb4143f86366b"}],"source":{"discovery":"UNKNOWN"},"title":"HTTP/2 header field values containing CR, LF or NUL are passed to the application unvalidated in Bandit"}},"cveMetadata":{"assignerOrgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","assignerShortName":"EEF","cveId":"CVE-2026-75484","datePublished":"2026-08-20T21:11:27.523Z","dateReserved":"2026-08-18T10:30:01.764Z","dateUpdated":"2026-08-20T21:11:27.523Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"}