{"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":"2026-09-21","sourceUpdated":"2026-09-21T17:17:36.663","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"}],"tags":["nvd","cve.org"],"cvssSource":"cna","ingestedAt":"2026-09-21T16:49:07.876Z","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.","depth":"midnight","depthScore":51,"depthScoreParts":{"impact":50.6,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}