{"id":"BIT-fluent-bit-2026-61674","summary":"Fluent Bit: Remote stack buffer overflow in Fluent Bit `out_forward` Secure-Forward `PONG` handler","details":"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.","aliases":["CVE-2026-61674","GHSA-jrp8-r9hx-gf73"],"modified":"2026-09-29T10:10:54.849897848Z","published":"2026-09-29T08:42:12.390Z","database_specific":{"severity":"Critical","cpes":["cpe:2.3:a:treasuredata:fluent_bit:*:*:*:*:*:*:*:*"]},"references":[{"type":"WEB","url":"https://github.com/fluent/fluent-bit/commit/45486556be9d023e194665e243f156b228e195e0"},{"type":"WEB","url":"https://github.com/fluent/fluent-bit/pull/11945"},{"type":"WEB","url":"https://github.com/fluent/fluent-bit/releases/tag/v5.0.8"},{"type":"WEB","url":"https://github.com/fluent/fluent-bit/security/advisories/GHSA-jrp8-r9hx-gf73"},{"type":"WEB","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-61674"}],"affected":[{"package":{"name":"fluent-bit","ecosystem":"Bitnami","purl":"pkg:bitnami/fluent-bit"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0.11.0"},{"fixed":"5.0.8"}]}],"database_specific":{"source":"https://github.com/bitnami/vulndb/tree/main/data/fluent-bit/BIT-fluent-bit-2026-61674.json"},"severity":[{"type":"CVSS_V4","score":"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/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X"}]}],"schema_version":"1.9.0"}