CVE-2026-43244 - Vulnerability Details

Vendors	Products
Linux	Linux Kernel

Link	Providers
https://git.kernel.org/stable/c/7af58f76e4b404a74c836881a845e6652db8a09f
https://git.kernel.org/stable/c/9ea3671d70ee07480d80bebe86696397c4e99fb7
https://git.kernel.org/stable/c/b1e3edf688a88c1a3ac41657055d9c136a08cd25
https://git.kernel.org/stable/c/ca220141fa8ebae09765a242076b2b77338106b0

Type	Values Removed	Values Added
Description		In the Linux kernel, the following vulnerability has been resolved: kcm: fix zero-frag skb in frag_list on partial sendmsg error Syzkaller reported a warning in kcm_write_msgs() when processing a message with a zero-fragment skb in the frag_list. When kcm_sendmsg() fills MAX_SKB_FRAGS fragments in the current skb, it allocates a new skb (tskb) and links it into the frag_list before copying data. If the copy subsequently fails (e.g. -EFAULT from user memory), tskb remains in the frag_list with zero fragments: head skb (msg being assembled, NOT yet in sk_write_queue) +-----------+ \| frags[17] \| (MAX_SKB_FRAGS, all filled with data) \| frag_list-+--> tskb +-----------+ +----------+ \| frags[0] \| (empty! copy failed before filling) +----------+ For SOCK_SEQPACKET with partial data already copied, the error path saves this message via partial_message for later completion. For SOCK_SEQPACKET, sock_write_iter() automatically sets MSG_EOR, so a subsequent zero-length write(fd, NULL, 0) completes the message and queues it to sk_write_queue. kcm_write_msgs() then walks the frag_list and hits: WARN_ON(!skb_shinfo(skb)->nr_frags) TCP has a similar pattern where skbs are enqueued before data copy and cleaned up on failure via tcp_remove_empty_skb(). KCM was missing the equivalent cleanup. Fix this by tracking the predecessor skb (frag_prev) when allocating a new frag_list entry. On error, if the tail skb has zero frags, use frag_prev to unlink and free it in O(1) without walking the singly-linked frag_list. frag_prev is safe to dereference because the entire message chain is only held locally (or in kcm->seq_skb) and is not added to sk_write_queue until MSG_EOR, so the send path cannot free it underneath us. Also change the WARN_ON to WARN_ON_ONCE to avoid flooding the log if the condition is somehow hit repeatedly. There are currently no KCM selftests in the kernel tree; a simple reproducer is available at [1]. [1] https://gist.github.com/mrpre/a94d431c757e8d6f168f4dd1a3749daa
Title		kcm: fix zero-frag skb in frag_list on partial sendmsg error
First Time appeared		Linux Linux linux Kernel
CPEs		cpe:2.3:o:linux:linux_kernel::::::::
Vendors & Products		Linux Linux linux Kernel
References		https://git.kernel.org/stable/c/7af58f76e4b404a74c836881a845e6652db8a09f https://git.kernel.org/stable/c/9ea3671d70ee07480d80bebe86696397c4e99fb7 https://git.kernel.org/stable/c/b1e3edf688a88c1a3ac41657055d9c136a08cd25 https://git.kernel.org/stable/c/ca220141fa8ebae09765a242076b2b77338106b0

{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-43244", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-05-01T14:12:55.995Z", "datePublished": "2026-05-06T11:28:36.946Z", "dateUpdated": "2026-05-06T11:28:36.946Z"}, "containers": {"cna": {"providerMetadata": {"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-05-06T11:28:36.946Z"}, "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"}], "affected": [{"product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["net/kcm/kcmsock.c"], "versions": [{"version": "ab7ac4eb9832e32a09f4e8042705484d2fb0aad3", "lessThan": "9ea3671d70ee07480d80bebe86696397c4e99fb7", "status": "affected", "versionType": "git"}, {"version": "ab7ac4eb9832e32a09f4e8042705484d2fb0aad3", "lessThan": "b1e3edf688a88c1a3ac41657055d9c136a08cd25", "status": "affected", "versionType": "git"}, {"version": "ab7ac4eb9832e32a09f4e8042705484d2fb0aad3", "lessThan": "7af58f76e4b404a74c836881a845e6652db8a09f", "status": "affected", "versionType": "git"}, {"version": "ab7ac4eb9832e32a09f4e8042705484d2fb0aad3", "lessThan": "ca220141fa8ebae09765a242076b2b77338106b0", "status": "affected", "versionType": "git"}]}, {"product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["net/kcm/kcmsock.c"], "versions": [{"version": "4.6", "status": "affected"}, {"version": "0", "lessThan": "4.6", "status": "unaffected", "versionType": "semver"}, {"version": "6.12.75", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver"}, {"version": "6.18.16", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver"}, {"version": "6.19.6", "lessThanOrEqual": "6.19.*", "status": "unaffected", "versionType": "semver"}, {"version": "7.0", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix"}]}], "cpeApplicability": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.6", "versionEndExcluding": "6.12.75"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.6", "versionEndExcluding": "6.18.16"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.6", "versionEndExcluding": "6.19.6"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.6", "versionEndExcluding": "7.0"}]}]}], "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"}}}}

{"cveTags": [], "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"}], "id": "CVE-2026-43244", "lastModified": "2026-05-06T13:07:51.607", "metrics": {}, "published": "2026-05-06T12:16:44.873", "references": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/7af58f76e4b404a74c836881a845e6652db8a09f"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/9ea3671d70ee07480d80bebe86696397c4e99fb7"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/b1e3edf688a88c1a3ac41657055d9c136a08cd25"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/ca220141fa8ebae09765a242076b2b77338106b0"}], "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "vulnStatus": "Awaiting Analysis"}

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