{"id":"CVE-2026-61674","aliases":["AZL-105060","BIT-fluent-bit-2026-61674","EUVD-2026-83985","GHSA-jrp8-r9hx-gf73"],"status":"published","title":"Fluent Bit: Remote stack buffer overflow in Fluent Bit `out_forward` Secure-Forward `PONG` handler","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.","severity":{"version":"4.0","score":9.2,"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","level":"critical","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-09","score":0.0072,"percentile":0.54188,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-121","CWE-787","CWE-843"],"published":"2026-09-21T16:10:15Z","modified":"2026-11-05T05:40:51Z","fixes":[{"ecosystem":"Azure Linux:3","package":"fluent-bit","fixed_in":["3.1.10-8"],"sources":["osv"]},{"ecosystem":"Bitnami","package":"fluent-bit","fixed_in":["5.0.8"],"sources":["osv"]}],"affected":[{"source":"osv","ecosystem":"Azure Linux:3","package":"fluent-bit","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.1.10-8"}]}]},{"source":"osv","ecosystem":"Bitnami","package":"fluent-bit","ranges":[{"type":"SEMVER","events":[{"introduced":"0.11.0"},{"fixed":"5.0.8"}]}]}],"products":[{"vendor":"fluent","product":"fluent-bit"},{"vendor":"microsoft","product":"fluent-bit"}],"references":[{"url":"https://github.com/fluent/fluent-bit/security/advisories/GHSA-jrp8-r9hx-gf73","tags":["x_refsource_CONFIRM","exploit","web","advisory"]},{"url":"https://github.com/fluent/fluent-bit/pull/11945","tags":["x_refsource_MISC","web","fix"]},{"url":"https://github.com/fluent/fluent-bit/commit/45486556be9d023e194665e243f156b228e195e0","tags":["x_refsource_MISC","web","fix"]},{"url":"https://github.com/fluent/fluent-bit/releases/tag/v5.0.8","tags":["x_refsource_MISC","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-61674","tags":["web","advisory"]},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/61xxx/CVE-2026-61674.json","tags":["advisory"]}],"sources":{"cve":[{"id":"CVE-2026-61674","title":"Fluent Bit: Remote stack buffer overflow in Fluent Bit `out_forward` Secure-Forward `PONG` handler","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.","status":"published","published":"2026-09-21T16:10:15.276Z","modified":"2026-09-21T18:52:25.84Z","cvss":[{"version":"4.0","score":9.2,"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","level":"critical","assessor":"cna"}],"cwes":["CWE-121","CWE-787","CWE-843"],"updated_at":"2026-11-02T14:19:53.786088Z"}],"euvd":[{"id":"EUVD-2026-83985","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.","status":"published","published":"2026-09-21T16:10:15Z","modified":"2026-09-21T18:52:25Z","cvss":[{"version":"4.0","score":9.2,"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","level":"critical"}],"updated_at":"2026-11-02T17:28:04.588371Z"}],"nvd":[{"id":"CVE-2026-61674","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.","status":"published","published":"2026-09-21T17:17:36.663Z","modified":"2026-09-24T21:16:28.12Z","cvss":[{"version":"4.0","score":9.2,"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/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","level":"critical","assessor":"secondary"}],"cwes":["CWE-121","CWE-787","CWE-843"],"updated_at":"2026-11-02T14:12:50.368368Z"}],"osv":[{"id":"CVE-2026-61674","title":"Fluent Bit: Remote stack buffer overflow in Fluent Bit `out_forward` Secure-Forward `PONG` handler","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.","status":"published","published":"2026-09-21T16:10:15.276Z","modified":"2026-10-28T11:18:19.701319146Z","cvss":[{"version":"4.0","score":9.2,"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","level":"critical"}],"cwes":["CWE-121","CWE-787","CWE-843"],"updated_at":"2026-11-02T15:45:12.933503Z"},{"id":"AZL-105060","title":"CVE-2026-61674 affecting package fluent-bit for versions less than 3.1.10-8","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.","status":"published","published":"2026-09-21T17:17:36Z","modified":"2026-11-05T05:40:51Z","updated_at":"2026-11-05T16:41:17.719431Z"},{"id":"BIT-fluent-bit-2026-61674","title":"Fluent Bit: Remote stack buffer overflow in Fluent Bit `out_forward` Secure-Forward `PONG` handler","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.","status":"published","published":"2026-09-29T08:42:12.39Z","modified":"2026-09-29T10:10:54.849897848Z","updated_at":"2026-11-02T15:28:29.563843Z"}]}}