{"api_version":"1","generated_at":"2026-05-13T08:51:25+00:00","cve":"CVE-2026-43121","urls":{"html":"https://cve.report/CVE-2026-43121","api":"https://cve.report/api/cve/CVE-2026-43121.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-43121","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-43121"},"summary":{"title":"io_uring/zcrx: fix user_ref race between scrub and refill paths","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nio_uring/zcrx: fix user_ref race between scrub and refill paths\n\nThe io_zcrx_put_niov_uref() function uses a non-atomic\ncheck-then-decrement pattern (atomic_read followed by separate\natomic_dec) to manipulate user_refs. This is serialized against other\ncallers by rq_lock, but io_zcrx_scrub() modifies the same counter with\natomic_xchg() WITHOUT holding rq_lock.\n\nOn SMP systems, the following race exists:\n\n  CPU0 (refill, holds rq_lock)          CPU1 (scrub, no rq_lock)\n  put_niov_uref:\n    atomic_read(uref) - 1\n    // window opens\n                                        atomic_xchg(uref, 0) - 1\n                                        return_niov_freelist(niov) [PUSH #1]\n    // window closes\n    atomic_dec(uref) - wraps to -1\n    returns true\n    return_niov(niov)\n    return_niov_freelist(niov)           [PUSH #2: DOUBLE-FREE]\n\nThe same niov is pushed to the freelist twice, causing free_count to\nexceed nr_iovs. Subsequent freelist pushes then perform an out-of-bounds\nwrite (a u32 value) past the kvmalloc'd freelist array into the adjacent\nslab object.\n\nFix this by replacing the non-atomic read-then-dec in\nio_zcrx_put_niov_uref() with an atomic_try_cmpxchg loop that atomically\ntests and decrements user_refs. This makes the operation safe against\nconcurrent atomic_xchg from scrub without requiring scrub to acquire\nrq_lock.\n\n[pavel: removed a warning and a comment]","state":"PUBLISHED","assigner":"Linux","published_at":"2026-05-06 12:16:28","updated_at":"2026-05-12 21:17:31"},"problem_types":["CWE-362"],"metrics":[{"version":"3.1","source":"nvd@nist.gov","type":"Primary","score":"4.7","severity":"MEDIUM","vector":"CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H","data":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H","baseScore":4.7,"baseSeverity":"MEDIUM","attackVector":"LOCAL","attackComplexity":"HIGH","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"NONE","integrityImpact":"NONE","availabilityImpact":"HIGH"}}],"references":[{"url":"https://git.kernel.org/stable/c/003049b1c4fb8aabb93febb7d1e49004f6ad653b","name":"https://git.kernel.org/stable/c/003049b1c4fb8aabb93febb7d1e49004f6ad653b","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":["Patch"],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/a94f096e28bfc7975163a6b80f1c8f323efe317a","name":"https://git.kernel.org/stable/c/a94f096e28bfc7975163a6b80f1c8f323efe317a","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":["Patch"],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/485dc691257b96e6d3bdc25b0eff2daadcc5c46c","name":"https://git.kernel.org/stable/c/485dc691257b96e6d3bdc25b0eff2daadcc5c46c","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":["Patch"],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-43121","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-43121","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 34a3e60821ab9f335a58d43a88cccdbefdebdec3 a94f096e28bfc7975163a6b80f1c8f323efe317a git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 34a3e60821ab9f335a58d43a88cccdbefdebdec3 485dc691257b96e6d3bdc25b0eff2daadcc5c46c git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 34a3e60821ab9f335a58d43a88cccdbefdebdec3 003049b1c4fb8aabb93febb7d1e49004f6ad653b git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 6.15","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.15 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.18.16 6.18.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.19.6 6.19.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.0 * original_commit_for_fix","platforms":[]}],"timeline":[],"solutions":[],"workarounds":[],"exploits":[],"credits":[],"nvd_cpes":[{"cve_year":"2026","cve_id":"43121","vulnerable":"1","versionEndIncluding":"","cpe1":"cpe","cpe2":"2.3","cpe3":"o","cpe4":"linux","cpe5":"linux_kernel","cpe6":"*","cpe7":"*","cpe8":"*","cpe9":"*","cpe10":"*","cpe11":"*","cpe12":"*","cpe13":"*"}],"vendor_comments":[],"enrichments":{"kev":null,"epss":null,"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"cna":{"affected":[{"defaultStatus":"unaffected","product":"Linux","programFiles":["io_uring/zcrx.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"lessThan":"a94f096e28bfc7975163a6b80f1c8f323efe317a","status":"affected","version":"34a3e60821ab9f335a58d43a88cccdbefdebdec3","versionType":"git"},{"lessThan":"485dc691257b96e6d3bdc25b0eff2daadcc5c46c","status":"affected","version":"34a3e60821ab9f335a58d43a88cccdbefdebdec3","versionType":"git"},{"lessThan":"003049b1c4fb8aabb93febb7d1e49004f6ad653b","status":"affected","version":"34a3e60821ab9f335a58d43a88cccdbefdebdec3","versionType":"git"}]},{"defaultStatus":"affected","product":"Linux","programFiles":["io_uring/zcrx.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"status":"affected","version":"6.15"},{"lessThan":"6.15","status":"unaffected","version":"0","versionType":"semver"},{"lessThanOrEqual":"6.18.*","status":"unaffected","version":"6.18.16","versionType":"semver"},{"lessThanOrEqual":"6.19.*","status":"unaffected","version":"6.19.6","versionType":"semver"},{"lessThanOrEqual":"*","status":"unaffected","version":"7.0","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.18.16","versionStartIncluding":"6.15","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.19.6","versionStartIncluding":"6.15","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.0","versionStartIncluding":"6.15","vulnerable":true}],"negate":false,"operator":"OR"}]}],"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nio_uring/zcrx: fix user_ref race between scrub and refill paths\n\nThe io_zcrx_put_niov_uref() function uses a non-atomic\ncheck-then-decrement pattern (atomic_read followed by separate\natomic_dec) to manipulate user_refs. This is serialized against other\ncallers by rq_lock, but io_zcrx_scrub() modifies the same counter with\natomic_xchg() WITHOUT holding rq_lock.\n\nOn SMP systems, the following race exists:\n\n  CPU0 (refill, holds rq_lock)          CPU1 (scrub, no rq_lock)\n  put_niov_uref:\n    atomic_read(uref) - 1\n    // window opens\n                                        atomic_xchg(uref, 0) - 1\n                                        return_niov_freelist(niov) [PUSH #1]\n    // window closes\n    atomic_dec(uref) - wraps to -1\n    returns true\n    return_niov(niov)\n    return_niov_freelist(niov)           [PUSH #2: DOUBLE-FREE]\n\nThe same niov is pushed to the freelist twice, causing free_count to\nexceed nr_iovs. Subsequent freelist pushes then perform an out-of-bounds\nwrite (a u32 value) past the kvmalloc'd freelist array into the adjacent\nslab object.\n\nFix this by replacing the non-atomic read-then-dec in\nio_zcrx_put_niov_uref() with an atomic_try_cmpxchg loop that atomically\ntests and decrements user_refs. This makes the operation safe against\nconcurrent atomic_xchg from scrub without requiring scrub to acquire\nrq_lock.\n\n[pavel: removed a warning and a comment]"}],"providerMetadata":{"dateUpdated":"2026-05-11T22:18:09.791Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"references":[{"url":"https://git.kernel.org/stable/c/a94f096e28bfc7975163a6b80f1c8f323efe317a"},{"url":"https://git.kernel.org/stable/c/485dc691257b96e6d3bdc25b0eff2daadcc5c46c"},{"url":"https://git.kernel.org/stable/c/003049b1c4fb8aabb93febb7d1e49004f6ad653b"}],"title":"io_uring/zcrx: fix user_ref race between scrub and refill paths","x_generator":{"engine":"bippy-1.2.0"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2026-43121","datePublished":"2026-05-06T11:27:08.216Z","dateReserved":"2026-05-01T14:12:55.987Z","dateUpdated":"2026-05-11T22:18:09.791Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-05-06 12:16:28","lastModifiedDate":"2026-05-12 21:17:31","problem_types":["CWE-362"],"metrics":{"cvssMetricV31":[{"source":"nvd@nist.gov","type":"Primary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H","baseScore":4.7,"baseSeverity":"MEDIUM","attackVector":"LOCAL","attackComplexity":"HIGH","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"NONE","integrityImpact":"NONE","availabilityImpact":"HIGH"},"exploitabilityScore":1,"impactScore":3.6}]},"configurations":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.15","versionEndExcluding":"6.18.16","matchCriteriaId":"5B5F989F-E891-48E4-9EC9-3C5EFD3DB9DC"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.19","versionEndExcluding":"6.19.6","matchCriteriaId":"373EEEDA-FAA1-4FB4-B6ED-DB4DD99DBE67"}]}]}]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"43121","Ordinal":"1","Title":"io_uring/zcrx: fix user_ref race between scrub and refill paths","CVE":"CVE-2026-43121","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"43121","Ordinal":"1","NoteData":"In the Linux kernel, the following vulnerability has been resolved:\n\nio_uring/zcrx: fix user_ref race between scrub and refill paths\n\nThe io_zcrx_put_niov_uref() function uses a non-atomic\ncheck-then-decrement pattern (atomic_read followed by separate\natomic_dec) to manipulate user_refs. This is serialized against other\ncallers by rq_lock, but io_zcrx_scrub() modifies the same counter with\natomic_xchg() WITHOUT holding rq_lock.\n\nOn SMP systems, the following race exists:\n\n  CPU0 (refill, holds rq_lock)          CPU1 (scrub, no rq_lock)\n  put_niov_uref:\n    atomic_read(uref) - 1\n    // window opens\n                                        atomic_xchg(uref, 0) - 1\n                                        return_niov_freelist(niov) [PUSH #1]\n    // window closes\n    atomic_dec(uref) - wraps to -1\n    returns true\n    return_niov(niov)\n    return_niov_freelist(niov)           [PUSH #2: DOUBLE-FREE]\n\nThe same niov is pushed to the freelist twice, causing free_count to\nexceed nr_iovs. Subsequent freelist pushes then perform an out-of-bounds\nwrite (a u32 value) past the kvmalloc'd freelist array into the adjacent\nslab object.\n\nFix this by replacing the non-atomic read-then-dec in\nio_zcrx_put_niov_uref() with an atomic_try_cmpxchg loop that atomically\ntests and decrements user_refs. This makes the operation safe against\nconcurrent atomic_xchg from scrub without requiring scrub to acquire\nrq_lock.\n\n[pavel: removed a warning and a comment]","Type":"Description","Title":"io_uring/zcrx: fix user_ref race between scrub and refill paths"}]}}}