{"id":"CVE-2026-61674","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-61674","generatedAt":"2026-10-28T01:51:05.884Z","title":"An attacker who controls or can impersonate an out_forward Secure Forward destination configured with Shared_Key or Empty_Shared_Key can send an oversized reason during the first handshake and overwrite stack control data.","description":"Fluent Bit is a fast and lightweight logs, metrics, and traces processor for Linux, BSD, macOS, and Windows. From 0.11.0 until 5.0.8, plugins/out_forward/forward.c secure_forward_pong copies the server-controlled PONG[2] reason into the 32-byte stack buffer msg with memcpy without checking its MessagePack type or length. An attacker who controls or can impersonate an out_forward Secure Forward destination configured with Shared_Key or Empty_Shared_Key can send an oversized reason during the first handshake and overwrite stack control data. Protected builds reliably terminate, while builds without a stack canary or with a disclosure can allow remote code execution as the Fluent Bit process user. When the opt-in --supervisor mode is used, fork-only respawns preserve the canary and address layout, allowing repeated crash-or-survive probes to support code execution on a hardened build; ordinary exec-based or service-manager restarts do not preserve that state. This issue is fixed in version 5.0.8.","published":"2026-09-21T17:17:37.000Z","lastModified":"2026-09-24T21:16:28.000Z","status":"Awaiting Analysis","sourceIdentifier":"security-advisories@github.com","cvss":{"version":"4.0","score":9.2,"severity":"CRITICAL","vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M"},"cwe":["CWE-121","CWE-787","CWE-843"],"affected":[],"epss":{"score":0.0072,"percentile":0.53638,"date":"2026-10-26","history":[{"date":"2026-09-22","score":0.00651,"percentile":0.49787}]},"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 (0.72%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit."},"changes":[{"kind":"new","label":"New CVE","at":"2026-09-21T17:17:37.000Z","detail":{"score":"9.2","severity":"CRITICAL","publishedAt":"2026-09-21T17:17:36.663Z"},"summary":"New CVE, critical severity (CVSS 9.2)."}],"references":[{"url":"https://github.com/fluent/fluent-bit/commit/45486556be9d023e194665e243f156b228e195e0","source":"security-advisories@github.com"},{"url":"https://github.com/fluent/fluent-bit/pull/11945","source":"security-advisories@github.com"},{"url":"https://github.com/fluent/fluent-bit/releases/tag/v5.0.8","source":"security-advisories@github.com"},{"url":"https://github.com/fluent/fluent-bit/security/advisories/GHSA-jrp8-r9hx-gf73","source":"security-advisories@github.com"},{"url":"https://github.com/fluent/fluent-bit/security/advisories/GHSA-jrp8-r9hx-gf73","source":"134c704f-9b21-4f2e-91b3-4a467353bcc0"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-61674","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."}