{"id":"CVE-2026-56386","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-56386","generatedAt":"2026-10-28T06:36:14.444Z","title":"Integer underflow and out-of-bounds read in the HTTP/2 server DATA frame parser in Apache bRPC allows an unauthenticated remote attacker to cause denial of service by sending a malformed DATA frame with the PADDED flag set and a zero-length payload.","description":"Integer underflow and out-of-bounds read in the HTTP/2 server DATA frame parser in Apache bRPC allows an unauthenticated remote attacker to cause denial of service by sending a malformed DATA frame with the PADDED flag set and a zero-length payload.\n\nRoot Cause:\nThe HTTP/2 DATA frame handler computed the fragment size from the attacker-controlled payload length and, when the PADDED flag was present, decremented the fragment size before ensuring that the frame contained the mandatory pad length byte. A zero-length padded DATA frame could therefore underflow the unsigned fragment size and read the pad length byte past the end of the frame buffer.\n\nAffected Scenarios:\nApache bRPC servers that accept HTTP/2 traffic are affected when a remote client can send crafted HTTP/2 frames to the server. HTTP/2 may be reached through cleartext h2c detection on an HTTP port or through TLS ALPN negotiation.\n\nHow to Fix:\n(Choose one of the following options)\n1. Upgrade Apache bRPC to version 1.18.0, which fixes this issue.\n2. Apply this patch:  https://github.com/apache/brpc/pull/3325 \n\nNote:\nThe fix validates that a padded DATA frame has enough payload bytes for the pad length field before decrementing the fragment size or reading the pad length byte. Malformed zero-length padded DATA frames are rejected with HTTP/2 FRAME_SIZE_ERROR.","published":"2026-10-21T12:17:21.000Z","lastModified":"2026-10-26T21:10:00.000Z","status":"Deferred","sourceIdentifier":"security@apache.org","cvss":{"version":"3.1","score":7.5,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},"cwe":["CWE-125","CWE-191"],"affected":[],"epss":{"score":0.00732,"percentile":0.54108,"date":"2026-10-27","history":[{"date":"2026-10-22","score":0.00732,"percentile":0.53783}]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"high","text":"High impact if exploited, but EPSS currently rates exploitation as unlikely (0.73%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit."},"changes":[{"kind":"scored","label":"Newly scored","at":"2026-10-21T19:02:43.000Z","detail":{"from":null,"score":"7.5","severity":"HIGH","fromSeverity":null},"summary":"Now scored CVSS 7.5 HIGH."},{"kind":"new","label":"New CVE","at":"2026-10-21T12:17:21.000Z","detail":{"score":null,"severity":null,"publishedAt":"2026-10-21T12:17:21.410Z"},"summary":"New CVE, high severity (CVSS 7.5)."}],"references":[{"url":"https://lists.apache.org/thread/2pf15ojj0vr7rtx95677kgtl1mx3gdgb","source":"security@apache.org"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-56386","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}