{"id":"CVE-2026-98084","title":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: backtracking shouldn't clear outer frame R1-R5 for callbacks\n\nWhen processing calls to bpf_loop() verifier marks R1 (and R4) as\nprecise","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: backtracking shouldn't clear outer frame R1-R5 for callbacks\n\nWhen processing calls to bpf_loop() verifier marks R1 (and R4) as\nprecise. R1 tracks loop iterations …","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= ab5cfac139ab8576fb54630d4cca23c3e690ee90 < f83890dfed9efc5e19df1dbc1ad707a142936923","Linux >= ab5cfac139ab8576fb54630d4cca23c3e690ee90 < e3e4f66cc4b72333d0886ae2673c360248987889","Linux b43550d7d58e7ae6618aaab18c1e912fa4d6e3dd","Linux >= 6.6.15 < 6.7","Linux 6.7"],"published":"2026-09-25","updated":"2026-09-25","sourceUpdated":"2026-09-25T11:17:37.980","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-98084","references":[{"url":"https://git.kernel.org/stable/c/e3e4f66cc4b72333d0886ae2673c360248987889","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/f83890dfed9efc5e19df1dbc1ad707a142936923","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"}],"tags":["nvd","cve.org"],"ingestedAt":"2026-09-25T11:06:38.835Z","slug":"CVE-2026-98084","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nbpf: backtracking shouldn't clear outer frame R1-R5 for callbacks\n\nWhen processing calls to bpf_loop() verifier marks R1 (and R4) as\nprecise. R1 tracks loop iterations number and because of the\n'callback_depth < R1' mechanics in check_helper_call() must be marked\nprecise. However, precision propagation for R1 was broken,\nwhen bpf_loop() call was verified on a second iteration.\n\nConsider the following verification trace:\n- main: bpf_loop(nr_loops, callback ...)\n- callback: BPF_EXIT\n- main: bpf_loop(nr_loops, callback ...)\n- ...\n\nWhile the first visit of the call to bpf_loop() propagated R1\nprecision as expected, the second call to mark_chain_precision() in\nthe check_helper_call() set R1, but it was immediately reset when\nbacktrack_insn() processed preceding BPF_EXIT in the loop deleted in\nthis patch.\n\nBecause of that, the second visit of the call to bpf_loop() injected\ncheckpoint with R1 not marked as precise. Which could trick the\nverifier into accepting unsafe programs. See the next patch for an\nexample of such program.\n\nCommit is structured in a way to minimize conflicts when\n'bpf' would be eventually merged with 'bpf-next'.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}