{"api_version":"1","generated_at":"2026-05-06T17:16:25+00:00","cve":"CVE-2026-43244","urls":{"html":"https://cve.report/CVE-2026-43244","api":"https://cve.report/api/cve/CVE-2026-43244.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-43244","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-43244"},"summary":{"title":"kcm: fix zero-frag skb in frag_list on partial sendmsg error","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nkcm: fix zero-frag skb in frag_list on partial sendmsg error\n\nSyzkaller reported a warning in kcm_write_msgs() when processing a\nmessage with a zero-fragment skb in the frag_list.\n\nWhen kcm_sendmsg() fills MAX_SKB_FRAGS fragments in the current skb,\nit allocates a new skb (tskb) and links it into the frag_list before\ncopying data. If the copy subsequently fails (e.g. -EFAULT from\nuser memory), tskb remains in the frag_list with zero fragments:\n\n  head skb (msg being assembled, NOT yet in sk_write_queue)\n  +-----------+\n  | frags[17] |  (MAX_SKB_FRAGS, all filled with data)\n  | frag_list-+--> tskb\n  +-----------+    +----------+\n                   | frags[0] |  (empty! copy failed before filling)\n                   +----------+\n\nFor SOCK_SEQPACKET with partial data already copied, the error path\nsaves this message via partial_message for later completion. For\nSOCK_SEQPACKET, sock_write_iter() automatically sets MSG_EOR, so a\nsubsequent zero-length write(fd, NULL, 0) completes the message and\nqueues it to sk_write_queue. kcm_write_msgs() then walks the\nfrag_list and hits:\n\n  WARN_ON(!skb_shinfo(skb)->nr_frags)\n\nTCP has a similar pattern where skbs are enqueued before data copy\nand cleaned up on failure via tcp_remove_empty_skb(). KCM was\nmissing the equivalent cleanup.\n\nFix this by tracking the predecessor skb (frag_prev) when allocating\na new frag_list entry. On error, if the tail skb has zero frags,\nuse frag_prev to unlink and free it in O(1) without walking the\nsingly-linked frag_list. frag_prev is safe to dereference because\nthe entire message chain is only held locally (or in kcm->seq_skb)\nand is not added to sk_write_queue until MSG_EOR, so the send path\ncannot free it underneath us.\n\nAlso change the WARN_ON to WARN_ON_ONCE to avoid flooding the log\nif the condition is somehow hit repeatedly.\n\nThere are currently no KCM selftests in the kernel tree; a simple\nreproducer is available at [1].\n\n[1] https://gist.github.com/mrpre/a94d431c757e8d6f168f4dd1a3749daa","state":"PUBLISHED","assigner":"Linux","published_at":"2026-05-06 12:16:44","updated_at":"2026-05-06 13:07:51"},"problem_types":[],"metrics":[],"references":[{"url":"https://git.kernel.org/stable/c/b1e3edf688a88c1a3ac41657055d9c136a08cd25","name":"https://git.kernel.org/stable/c/b1e3edf688a88c1a3ac41657055d9c136a08cd25","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/ca220141fa8ebae09765a242076b2b77338106b0","name":"https://git.kernel.org/stable/c/ca220141fa8ebae09765a242076b2b77338106b0","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/7af58f76e4b404a74c836881a845e6652db8a09f","name":"https://git.kernel.org/stable/c/7af58f76e4b404a74c836881a845e6652db8a09f","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/9ea3671d70ee07480d80bebe86696397c4e99fb7","name":"https://git.kernel.org/stable/c/9ea3671d70ee07480d80bebe86696397c4e99fb7","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-43244","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-43244","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected ab7ac4eb9832e32a09f4e8042705484d2fb0aad3 9ea3671d70ee07480d80bebe86696397c4e99fb7 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected ab7ac4eb9832e32a09f4e8042705484d2fb0aad3 b1e3edf688a88c1a3ac41657055d9c136a08cd25 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected ab7ac4eb9832e32a09f4e8042705484d2fb0aad3 7af58f76e4b404a74c836881a845e6652db8a09f git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected ab7ac4eb9832e32a09f4e8042705484d2fb0aad3 ca220141fa8ebae09765a242076b2b77338106b0 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 4.6","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 4.6 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.12.75 6.12.* 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":[],"vendor_comments":[],"enrichments":{"kev":null,"epss":null,"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"cna":{"affected":[{"defaultStatus":"unaffected","product":"Linux","programFiles":["net/kcm/kcmsock.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"lessThan":"9ea3671d70ee07480d80bebe86696397c4e99fb7","status":"affected","version":"ab7ac4eb9832e32a09f4e8042705484d2fb0aad3","versionType":"git"},{"lessThan":"b1e3edf688a88c1a3ac41657055d9c136a08cd25","status":"affected","version":"ab7ac4eb9832e32a09f4e8042705484d2fb0aad3","versionType":"git"},{"lessThan":"7af58f76e4b404a74c836881a845e6652db8a09f","status":"affected","version":"ab7ac4eb9832e32a09f4e8042705484d2fb0aad3","versionType":"git"},{"lessThan":"ca220141fa8ebae09765a242076b2b77338106b0","status":"affected","version":"ab7ac4eb9832e32a09f4e8042705484d2fb0aad3","versionType":"git"}]},{"defaultStatus":"affected","product":"Linux","programFiles":["net/kcm/kcmsock.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"status":"affected","version":"4.6"},{"lessThan":"4.6","status":"unaffected","version":"0","versionType":"semver"},{"lessThanOrEqual":"6.12.*","status":"unaffected","version":"6.12.75","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":"6.12.75","versionStartIncluding":"4.6","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.18.16","versionStartIncluding":"4.6","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.19.6","versionStartIncluding":"4.6","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.0","versionStartIncluding":"4.6","vulnerable":true}],"negate":false,"operator":"OR"}]}],"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nkcm: fix zero-frag skb in frag_list on partial sendmsg error\n\nSyzkaller reported a warning in kcm_write_msgs() when processing a\nmessage with a zero-fragment skb in the frag_list.\n\nWhen kcm_sendmsg() fills MAX_SKB_FRAGS fragments in the current skb,\nit allocates a new skb (tskb) and links it into the frag_list before\ncopying data. If the copy subsequently fails (e.g. -EFAULT from\nuser memory), tskb remains in the frag_list with zero fragments:\n\n  head skb (msg being assembled, NOT yet in sk_write_queue)\n  +-----------+\n  | frags[17] |  (MAX_SKB_FRAGS, all filled with data)\n  | frag_list-+--> tskb\n  +-----------+    +----------+\n                   | frags[0] |  (empty! copy failed before filling)\n                   +----------+\n\nFor SOCK_SEQPACKET with partial data already copied, the error path\nsaves this message via partial_message for later completion. For\nSOCK_SEQPACKET, sock_write_iter() automatically sets MSG_EOR, so a\nsubsequent zero-length write(fd, NULL, 0) completes the message and\nqueues it to sk_write_queue. kcm_write_msgs() then walks the\nfrag_list and hits:\n\n  WARN_ON(!skb_shinfo(skb)->nr_frags)\n\nTCP has a similar pattern where skbs are enqueued before data copy\nand cleaned up on failure via tcp_remove_empty_skb(). KCM was\nmissing the equivalent cleanup.\n\nFix this by tracking the predecessor skb (frag_prev) when allocating\na new frag_list entry. On error, if the tail skb has zero frags,\nuse frag_prev to unlink and free it in O(1) without walking the\nsingly-linked frag_list. frag_prev is safe to dereference because\nthe entire message chain is only held locally (or in kcm->seq_skb)\nand is not added to sk_write_queue until MSG_EOR, so the send path\ncannot free it underneath us.\n\nAlso change the WARN_ON to WARN_ON_ONCE to avoid flooding the log\nif the condition is somehow hit repeatedly.\n\nThere are currently no KCM selftests in the kernel tree; a simple\nreproducer is available at [1].\n\n[1] https://gist.github.com/mrpre/a94d431c757e8d6f168f4dd1a3749daa"}],"providerMetadata":{"dateUpdated":"2026-05-06T11:28:36.946Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"references":[{"url":"https://git.kernel.org/stable/c/9ea3671d70ee07480d80bebe86696397c4e99fb7"},{"url":"https://git.kernel.org/stable/c/b1e3edf688a88c1a3ac41657055d9c136a08cd25"},{"url":"https://git.kernel.org/stable/c/7af58f76e4b404a74c836881a845e6652db8a09f"},{"url":"https://git.kernel.org/stable/c/ca220141fa8ebae09765a242076b2b77338106b0"}],"title":"kcm: fix zero-frag skb in frag_list on partial sendmsg error","x_generator":{"engine":"bippy-1.2.0"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2026-43244","datePublished":"2026-05-06T11:28:36.946Z","dateReserved":"2026-05-01T14:12:55.995Z","dateUpdated":"2026-05-06T11:28:36.946Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-05-06 12:16:44","lastModifiedDate":"2026-05-06 13:07:51","problem_types":[],"metrics":[],"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"43244","Ordinal":"1","Title":"kcm: fix zero-frag skb in frag_list on partial sendmsg error","CVE":"CVE-2026-43244","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"43244","Ordinal":"1","NoteData":"In the Linux kernel, the following vulnerability has been resolved:\n\nkcm: fix zero-frag skb in frag_list on partial sendmsg error\n\nSyzkaller reported a warning in kcm_write_msgs() when processing a\nmessage with a zero-fragment skb in the frag_list.\n\nWhen kcm_sendmsg() fills MAX_SKB_FRAGS fragments in the current skb,\nit allocates a new skb (tskb) and links it into the frag_list before\ncopying data. If the copy subsequently fails (e.g. -EFAULT from\nuser memory), tskb remains in the frag_list with zero fragments:\n\n  head skb (msg being assembled, NOT yet in sk_write_queue)\n  +-----------+\n  | frags[17] |  (MAX_SKB_FRAGS, all filled with data)\n  | frag_list-+--> tskb\n  +-----------+    +----------+\n                   | frags[0] |  (empty! copy failed before filling)\n                   +----------+\n\nFor SOCK_SEQPACKET with partial data already copied, the error path\nsaves this message via partial_message for later completion. For\nSOCK_SEQPACKET, sock_write_iter() automatically sets MSG_EOR, so a\nsubsequent zero-length write(fd, NULL, 0) completes the message and\nqueues it to sk_write_queue. kcm_write_msgs() then walks the\nfrag_list and hits:\n\n  WARN_ON(!skb_shinfo(skb)->nr_frags)\n\nTCP has a similar pattern where skbs are enqueued before data copy\nand cleaned up on failure via tcp_remove_empty_skb(). KCM was\nmissing the equivalent cleanup.\n\nFix this by tracking the predecessor skb (frag_prev) when allocating\na new frag_list entry. On error, if the tail skb has zero frags,\nuse frag_prev to unlink and free it in O(1) without walking the\nsingly-linked frag_list. frag_prev is safe to dereference because\nthe entire message chain is only held locally (or in kcm->seq_skb)\nand is not added to sk_write_queue until MSG_EOR, so the send path\ncannot free it underneath us.\n\nAlso change the WARN_ON to WARN_ON_ONCE to avoid flooding the log\nif the condition is somehow hit repeatedly.\n\nThere are currently no KCM selftests in the kernel tree; a simple\nreproducer is available at [1].\n\n[1] https://gist.github.com/mrpre/a94d431c757e8d6f168f4dd1a3749daa","Type":"Description","Title":"kcm: fix zero-frag skb in frag_list on partial sendmsg error"}]}}}