{"id":"CVE-2026-98061","title":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Reject tail calls directly from callback frames\n\nA tail call from a non-zero frame is modeled as a return from that frame.\nThe verifier makes R0 unknown and calls …","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Reject tail calls directly from callback frames\n\nA tail call from a non-zero frame is modeled as a return from that frame.\nThe verifier makes R0 unknown and calls …","severity":"medium","cvss":5.5,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","cwe":["CWE-617"],"vendor":"Linux","product":"Linux","affected":["Linux >= a6c22c91b6284e4713c0cf5b20ab3c9c71b77ae8 < 617c8266e49f45747f71e74177646a63f72b7025","Linux >= e3245f8990431950d20631c72236d4e8cb2dcde8 < 96d31b28263c429a56e4de85bcf744a5c320b3a3","Linux >= e3245f8990431950d20631c72236d4e8cb2dcde8 < 266aa4ad0b2e82397cd9045752c9bff03d98eddd","Linux >= 6.18.2 < 6.18.53","Linux 6.19"],"published":"2026-09-25","updated":"2026-09-30","sourceUpdated":"2026-09-30T14:10:59.253","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-98061","references":[{"url":"https://git.kernel.org/stable/c/266aa4ad0b2e82397cd9045752c9bff03d98eddd","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/617c8266e49f45747f71e74177646a63f72b7025","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/96d31b28263c429a56e4de85bcf744a5c320b3a3","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-98061.json"},{"url":"https://access.redhat.com/security/cve/CVE-2026-98061"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2541124"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-98061"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98061"},{"url":"https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-98061.mbox"}],"tags":["nvd","cve.org","csaf","vex","red-hat"],"epss":0.00198,"epssPercentile":0.09526,"cvssSource":"vendor","ingestedAt":"2026-09-25T11:06:38.843Z","slug":"CVE-2026-98061","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Reject tail calls directly from callback frames\n\nA tail call from a non-zero frame is modeled as a return from that frame.\nThe verifier makes R0 unknown and calls prepare_func_exit() for the taken\nbranch.\n\nWhen the current frame is a synchronous callback, prepare_func_exit()\nenforces the callback return-value contract and marks R0 precise. Since the\ntail-call path synthesized R0 rather than deriving it from an instruction,\nprecision backtracking reaches the callback-calling instruction with R0\nstill requested and triggers the \"callback unexpected regs\" verifier bug.\nA CAP_BPF task can therefore cause a WARN and an -EFAULT BPF_PROG_LOAD.\n\nTail calls reachable from callbacks are already rejected later by\ncheck_max_stack_depth(). Reject a tail call made directly by a callback\nbefore constructing the inconsistent return state, using the existing\ndiagnostic. Tail calls from ordinary subprograms keep their current\nbehavior.\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** · Low · affected: Red Hat Enterprise Linux 10 · no fix planned: Red Hat Enterprise Linux 10 · updated 2026-10-17 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-98061.json)","depth":"sunlit","depthScore":30,"depthScoreParts":{"impact":30.3,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[{"seq":212380,"id":"CVE-2026-98061","ts":1790668160630,"field":"cvss","old":null,"new":"5.5"},{"seq":212379,"id":"CVE-2026-98061","ts":1790668160630,"field":"severity","old":"none","new":"medium"}]}