{"schema":"threatline.record/2","record":{"id":"CVE-2026-84897","aliases":[],"summary":"wolfSSH server accepts server-to-client DH group exchange messages from an unauthenticated client, causing pre-authentication primality-test CPU exhaustion and key exchange role confusion","details":"src/internal.c in wolfSSL wolfSSH through 1.5.0 admits the server-to-client Diffie-Hellman group exchange messages SSH_MSG_KEX_DH_GEX_GROUP (31) and SSH_MSG_KEX_DH_GEX_REPLY (33) when a server receives them from an unauthenticated client. IsMessageAllowedServer() applies no direction check to the key exchange message range: when the peer is keying and no particular message is expected, which is the state a server is in for the whole window after it processes the client's KEXINIT because nothing sets handshake->expectMsgId there, the function falls out of its expectation branch without a verdict and reaches a numeric bound that admits every message id from 30 through 34. A client that negotiates diffie-hellman-group-exchange-sha256 and then sends message 31 makes the server run the client-side handler DoKexDhGexGroup(), which validates the attacker-supplied group with two 8-round Miller-Rabin primality tests, one on p and one on (p-1)/2, on a value of up to 8192 bits. The handler then returns success: the server stores the attacker's prime and generator, generates a Diffie-Hellman key pair in the attacker's group, and sends the client-role message SSH_MSG_KEX_DH_GEX_INIT (32) back to the attacker. Published RFC 3526 safe primes are the worst-case input and cost the attacker nothing to obtain. The primality validation was added in 1.5.0; versions from 1.2.0 through 1.4.22 admit the same message and enter the same client-role path without the primality cost. Message 33 is admitted as well, but on a server it is rejected before any cryptography because no public key check callback is registered, so it carries no comparable cost. Builds that define WOLFSSH_NO_DH_GEX_SHA256, which is implied by WOLFSSH_NO_DH or NO_SHA256, are unaffected.","categories":["Unclassified"],"product":"wolfSSH","vendor":"wolfSSL Inc.","ecosystem":null,"affected_ranges":[{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-84897","source_modified_at":"2026-10-07T18:37:00.316Z","fetched_at":"2026-10-23T18:48:36.087640Z","product":"wolfSSH","vendor":"wolfSSL Inc.","versions":[{"status":"affected","version":"1.2.0","lessThanOrEqual":"1.5.0","changes":[{"at":"1.6.0","status":"unaffected"}],"versionType":"semver"}],"defaultStatus":"unaffected"}],"fixed_versions":[],"cvss":6.9,"severity":"Medium","kev":{"listed":false},"epss":{"probability":0.00301,"percentile":0.21705,"score_date":"2026-10-23"},"published_at":"2026-10-07T02:42:28.388Z","modified_at":"2026-10-07T18:37:00.316Z","provenance":[{"source":"CVE List","url":"https://www.cve.org/CVERecord?id=CVE-2026-84897","fetched_at":"2026-10-23T18:48:36.087640Z","source_modified_at":"2026-10-07T18:37:00.316Z"},{"source":"EPSS","url":"https://api.first.org/data/v1/epss?cve=CVE-2026-84897","fetched_at":"2026-10-23T18:42:43.628194Z","source_modified_at":"2026-10-23"}],"sources":["CVE List","EPSS"],"references":[{"source":"CVE List","url":"https://github.com/wolfSSL/wolfssh/pull/1221","tags":["patch"]},{"source":"CVE List","url":"https://github.com/wolfSSL/wolfssh/commit/a472f1ee2b653f623d85ef2297321733f1dbfd22","tags":["patch"]},{"source":"CVE List","url":"https://www.rfc-editor.org/rfc/rfc4419.html","tags":["technical-description"]},{"source":"CVE List","url":"https://www.rfc-editor.org/rfc/rfc3526.html","tags":["technical-description"]}],"locations":[],"motoko_assessment":{"status":"requires_architecture_review","automatic_remediation":false},"cve_state":"PUBLISHED","cvss_source":"CVE List","ssvc":{"exploitation":"none","automatable":"yes","technical_impact":"partial","assessed_at":"2026-10-07T18:36:45.750446Z"},"classification":{"method":"product-first software-layer rules","rules_version":"2.1","matched_on":null,"confidence":"unknown","reviewed":false},"change_timestamp":"2026-10-07T18:37:00.316Z","content_hash":"287c77e899a4479c5bd7440c459803e34fb2dd83690827028539890460d38f64"}}