{"id":"CVE-2026-61674","title":"Fluent Bit is a fast and lightweight logs, metrics, and traces processor for Linux, BSD, macOS, and Windows","summary":"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 …","severity":"critical","cvss":9.2,"cvssVector":"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","cwe":["CWE-121","CWE-787","CWE-843"],"vendor":"fluent","product":"fluent-bit","affected":["fluent-bit >= 0.11.0, < 5.0.8"],"published":"2026-09-21","updated":"2026-09-24","sourceUpdated":"2026-09-24T21:16:28.120","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-61674","references":[{"url":"https://github.com/fluent/fluent-bit/commit/45486556be9d023e194665e243f156b228e195e0","label":"security-advisories@github.com"},{"url":"https://github.com/fluent/fluent-bit/pull/11945","label":"security-advisories@github.com"},{"url":"https://github.com/fluent/fluent-bit/releases/tag/v5.0.8","label":"security-advisories@github.com"},{"url":"https://github.com/fluent/fluent-bit/security/advisories/GHSA-jrp8-r9hx-gf73","label":"security-advisories@github.com"},{"url":"https://github.com/fluent/fluent-bit/security/advisories/GHSA-jrp8-r9hx-gf73","label":"134c704f-9b21-4f2e-91b3-4a467353bcc0"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-61674.json"},{"url":"https://access.redhat.com/security/cve/CVE-2026-61674"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-61674"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-61674"}],"tags":["nvd","cve.org","exploit-available","csaf","vex","red-hat"],"epss":0.0072,"epssPercentile":0.53708,"exploitAvailable":true,"ssvc":{"exploitation":"poc","automatable":"no","technicalImpact":"total","timestamp":"2026-09-21T18:51:32.206511Z"},"cvssSource":"cna","ingestedAt":"2026-09-21T16:49:07.876Z","scores":{"cna":9.2,"vendor":8.1},"slug":"CVE-2026-61674","body":"## Overview\n\nFluent 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.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.\n\n## Vendor advisories\n\n- **Red Hat VEX** · updated 2026-10-16 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-61674.json)","depth":"abyssal","depthScore":63,"depthScoreParts":{"impact":50.6,"likelihood":0.1,"exploitation":12,"ransomware":0},"changes":[{"seq":208759,"id":"CVE-2026-61674","ts":1790020359238,"field":"exploit_available","old":"false","new":"true"}]}