# CVE-2026-43244: kcm: fix zero-frag skb in frag_list on partial sendmsg error

CVE-2026-43244 is fixed in 60 products on 1 platform, first by ALAS2023-2026-1543, released April 7, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-43244
- Priority: Routine
- CVSS: 5.5 (Moderate)
- EPSS: 0.0016
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Apr 7, 2026
- Weakness: Missing Release of Memory after Effective Lifetime
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-43244

## 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

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | bpftool6.12 amzn 2023 | 1:6.12.77-99.140.amzn2023 | [ALAS2023-2026-1543](https://patchblox.com/security/data/fix/linux/alas2023-2026-1543.md) | Apr 7, 2026 |
| Linux | bpftool6.12-debuginfo amzn 2023 | 1:6.12.77-99.140.amzn2023 | [ALAS2023-2026-1543](https://patchblox.com/security/data/fix/linux/alas2023-2026-1543.md) | Apr 7, 2026 |
| Linux | bpftool6.18 amzn 2023 | 1:6.18.16-18.222.amzn2023 | [ALAS2023-2026-1702](https://patchblox.com/security/data/fix/linux/alas2023-2026-1702.md) | May 11, 2026 |
| Linux | bpftool6.18-debuginfo amzn 2023 | 1:6.18.16-18.222.amzn2023 | [ALAS2023-2026-1702](https://patchblox.com/security/data/fix/linux/alas2023-2026-1702.md) | May 11, 2026 |
| Linux | dtb-aarch64 opensuse-leap 16.0 | 6.12.0-160000.37.1 | [OPENSUSE-SU-2026:21555-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21555-1.md) | Aug 12, 2026 |
| Linux | kernel-64kb opensuse-leap 16.0 | 6.12.0-160000.37.1 | [OPENSUSE-SU-2026:21555-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21555-1.md) | Aug 12, 2026 |
| Linux | kernel-64kb sles 15.7 | 6.4.0-150700.53.73.2 | [SUSE-SU-2026:3166-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-3166-1.md) | Jul 21, 2026 |
| Linux | kernel-64kb sles 16.0 | 6.12.0-160000.37.1 | [SUSE-SU-2026:23231-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-23231-1.md) | Aug 11, 2026 |
| Linux | kernel-azure opensuse-leap 16.0 | 6.12.0-160000.37.1 | [OPENSUSE-SU-2026:21555-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21555-1.md) | Aug 12, 2026 |
| Linux | kernel-azure sles 15.7 | 6.4.0-150700.53.73.2 | [SUSE-SU-2026:3166-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-3166-1.md) | Jul 21, 2026 |
| Linux | kernel-azure sles 16.0 | 6.12.0-160000.37.1 | [SUSE-SU-2026:23231-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-23231-1.md) | Aug 11, 2026 |
| Linux | kernel-default opensuse-leap 16.0 | 6.12.0-160000.37.1 | [OPENSUSE-SU-2026:21555-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21555-1.md) | Aug 12, 2026 |
| Linux | kernel-default sles 15.7 | 6.4.0-150700.53.73.2 | [SUSE-SU-2026:3166-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-3166-1.md) | Jul 21, 2026 |
| Linux | kernel-default sles 16.0 | 6.12.0-160000.37.1 | [SUSE-SU-2026:23237-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-23237-1.md) | Aug 11, 2026 |
| Linux | kernel-default-base opensuse-leap 16.0 | 6.12.0-160000.37.1.160000.2.19 | [OPENSUSE-SU-2026:21555-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21555-1.md) | Aug 12, 2026 |
| Linux | kernel-default-base sles 15.7 | 6.4.0-150700.53.73.2.150700.17.41.4 | [SUSE-SU-2026:3166-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-3166-1.md) | Jul 21, 2026 |
| Linux | kernel-default-base sles 16.0 | 6.12.0-160000.37.1.160000.2.19 | [SUSE-SU-2026:23231-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-23231-1.md) | Aug 11, 2026 |
| Linux | kernel-docs opensuse-leap 16.0 | 6.12.0-160000.37.1 | [OPENSUSE-SU-2026:21555-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21555-1.md) | Aug 12, 2026 |
| Linux | kernel-docs sles 15.7 | 6.4.0-150700.53.73.1 | [SUSE-SU-2026:3166-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-3166-1.md) | Jul 21, 2026 |
| Linux | kernel-docs sles 16.0 | 6.12.0-160000.37.1 | [SUSE-SU-2026:23231-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-23231-1.md) | Aug 11, 2026 |
| Linux | kernel-kvmsmall opensuse-leap 16.0 | 6.12.0-160000.37.1 | [OPENSUSE-SU-2026:21555-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21555-1.md) | Aug 12, 2026 |
| Linux | kernel-kvmsmall sles 16.0 | 6.12.0-160000.37.1 | [SUSE-SU-2026:23231-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-23231-1.md) | Aug 11, 2026 |
| Linux | kernel-livepatch-6.12.77-99.140 amzn 2023 | 1:1.0-0.amzn2023 | [ALAS2023-2026-1543](https://patchblox.com/security/data/fix/linux/alas2023-2026-1543.md) | Apr 7, 2026 |
| Linux | kernel-livepatch-6.18.16-18.222 amzn 2023 | 1:1.0-0.amzn2023 | [ALAS2023-2026-1702](https://patchblox.com/security/data/fix/linux/alas2023-2026-1702.md) | May 11, 2026 |
| Linux | kernel-livepatch-SLE15-SP7-RT_Update_18 sles 15.7 | 1-150700.1.5.1 | [SUSE-SU-2026:3130-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-3130-1.md) | Jul 20, 2026 |
| Linux | kernel-livepatch-SLE15-SP7_Update_19 sles 15.7 | 1-150700.15.3.4 | [SUSE-SU-2026:3166-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-3166-1.md) | Jul 21, 2026 |
| Linux | kernel-obs-build opensuse-leap 16.0 | 6.12.0-160000.37.1 | [OPENSUSE-SU-2026:21555-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21555-1.md) | Aug 12, 2026 |
| Linux | kernel-obs-build sles 15.7 | 6.4.0-150700.53.73.2 | [SUSE-SU-2026:3166-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-3166-1.md) | Jul 21, 2026 |
| Linux | kernel-obs-qa opensuse-leap 16.0 | 6.12.0-160000.37.1 | [OPENSUSE-SU-2026:21555-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21555-1.md) | Aug 12, 2026 |
| Linux | kernel-obs-qa sles 16.0 | 6.12.0-160000.37.1 | [SUSE-SU-2026:23231-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-23231-1.md) | Aug 11, 2026 |
| Linux | kernel-rt opensuse-leap 16.0 | 6.12.0-160000.37.1 | [OPENSUSE-SU-2026:21555-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21555-1.md) | Aug 12, 2026 |
| Linux | kernel-source opensuse-leap 16.0 | 6.12.0-160000.37.1 | [OPENSUSE-SU-2026:21555-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21555-1.md) | Aug 12, 2026 |
| Linux | kernel-source sles 15.7 | 6.4.0-150700.53.73.1 | [SUSE-SU-2026:3166-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-3166-1.md) | Jul 21, 2026 |
| Linux | kernel-source sles 16.0 | 6.12.0-160000.37.1 | [SUSE-SU-2026:23231-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-23231-1.md) | Aug 11, 2026 |
| Linux | kernel-syms opensuse-leap 16.0 | 6.12.0-160000.37.1 | [OPENSUSE-SU-2026:21555-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21555-1.md) | Aug 12, 2026 |
| Linux | kernel-syms sles 15.7 | 6.4.0-150700.53.73.1 | [SUSE-SU-2026:3166-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-3166-1.md) | Jul 21, 2026 |
| Linux | kernel-syms sles 16.0 | 6.12.0-160000.37.1 | [SUSE-SU-2026:23231-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-23231-1.md) | Aug 11, 2026 |
| Linux | kernel-zfcpdump opensuse-leap 16.0 | 6.12.0-160000.37.1 | [OPENSUSE-SU-2026:21555-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21555-1.md) | Aug 12, 2026 |
| Linux | kernel-zfcpdump sles 15.7 | 6.4.0-150700.53.73.2 | [SUSE-SU-2026:3166-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-3166-1.md) | Jul 21, 2026 |
| Linux | kernel-zfcpdump sles 16.0 | 6.12.0-160000.37.1 | [SUSE-SU-2026:23231-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-23231-1.md) | Aug 11, 2026 |
| Linux | kernel6.12 amzn 2023 | 1:6.12.77-99.140.amzn2023 | [ALAS2023-2026-1543](https://patchblox.com/security/data/fix/linux/alas2023-2026-1543.md) | Apr 7, 2026 |
| Linux | kernel6.12-debuginfo amzn 2023 | 1:6.12.77-99.140.amzn2023 | [ALAS2023-2026-1543](https://patchblox.com/security/data/fix/linux/alas2023-2026-1543.md) | Apr 7, 2026 |
| Linux | kernel6.12-debuginfo-common-aarch64 amzn 2023 | 1:6.12.77-99.140.amzn2023 | [ALAS2023-2026-1543](https://patchblox.com/security/data/fix/linux/alas2023-2026-1543.md) | Apr 7, 2026 |
| Linux | kernel6.12-debuginfo-common-x86_64 amzn 2023 | 1:6.12.77-99.140.amzn2023 | [ALAS2023-2026-1543](https://patchblox.com/security/data/fix/linux/alas2023-2026-1543.md) | Apr 7, 2026 |
| Linux | kernel6.12-devel amzn 2023 | 1:6.12.77-99.140.amzn2023 | [ALAS2023-2026-1543](https://patchblox.com/security/data/fix/linux/alas2023-2026-1543.md) | Apr 7, 2026 |
| Linux | kernel6.12-headers amzn 2023 | 1:6.12.77-99.140.amzn2023 | [ALAS2023-2026-1543](https://patchblox.com/security/data/fix/linux/alas2023-2026-1543.md) | Apr 7, 2026 |
| Linux | kernel6.12-libbpf amzn 2023 | 1:6.12.77-99.140.amzn2023 | [ALAS2023-2026-1543](https://patchblox.com/security/data/fix/linux/alas2023-2026-1543.md) | Apr 7, 2026 |
| Linux | kernel6.12-libbpf-debuginfo amzn 2023 | 1:6.12.77-99.140.amzn2023 | [ALAS2023-2026-1543](https://patchblox.com/security/data/fix/linux/alas2023-2026-1543.md) | Apr 7, 2026 |
| Linux | kernel6.12-libbpf-devel amzn 2023 | 1:6.12.77-99.140.amzn2023 | [ALAS2023-2026-1543](https://patchblox.com/security/data/fix/linux/alas2023-2026-1543.md) | Apr 7, 2026 |
| Linux | kernel6.12-libbpf-static amzn 2023 | 1:6.12.77-99.140.amzn2023 | [ALAS2023-2026-1543](https://patchblox.com/security/data/fix/linux/alas2023-2026-1543.md) | Apr 7, 2026 |
| Linux | kernel6.12-modules-extra amzn 2023 | 1:6.12.77-99.140.amzn2023 | [ALAS2023-2026-1543](https://patchblox.com/security/data/fix/linux/alas2023-2026-1543.md) | Apr 7, 2026 |
| Linux | kernel6.12-modules-extra-common amzn 2023 | 1:6.12.77-99.140.amzn2023 | [ALAS2023-2026-1543](https://patchblox.com/security/data/fix/linux/alas2023-2026-1543.md) | Apr 7, 2026 |
| Linux | kernel6.12-tools amzn 2023 | 1:6.12.77-99.140.amzn2023 | [ALAS2023-2026-1543](https://patchblox.com/security/data/fix/linux/alas2023-2026-1543.md) | Apr 7, 2026 |
| Linux | kernel6.12-tools-debuginfo amzn 2023 | 1:6.12.77-99.140.amzn2023 | [ALAS2023-2026-1543](https://patchblox.com/security/data/fix/linux/alas2023-2026-1543.md) | Apr 7, 2026 |
| Linux | kernel6.12-tools-devel amzn 2023 | 1:6.12.77-99.140.amzn2023 | [ALAS2023-2026-1543](https://patchblox.com/security/data/fix/linux/alas2023-2026-1543.md) | Apr 7, 2026 |
| Linux | kernel6.18 amzn 2023 | 1:6.18.16-18.222.amzn2023 | [ALAS2023-2026-1702](https://patchblox.com/security/data/fix/linux/alas2023-2026-1702.md) | May 11, 2026 |
| Linux | kernel6.18-debuginfo amzn 2023 | 1:6.18.16-18.222.amzn2023 | [ALAS2023-2026-1702](https://patchblox.com/security/data/fix/linux/alas2023-2026-1702.md) | May 11, 2026 |
| Linux | kernel6.18-debuginfo-common-aarch64 amzn 2023 | 1:6.18.16-18.222.amzn2023 | [ALAS2023-2026-1702](https://patchblox.com/security/data/fix/linux/alas2023-2026-1702.md) | May 11, 2026 |
| Linux | kernel6.18-debuginfo-common-x86_64 amzn 2023 | 1:6.18.16-18.222.amzn2023 | [ALAS2023-2026-1702](https://patchblox.com/security/data/fix/linux/alas2023-2026-1702.md) | May 11, 2026 |
| Linux | kernel6.18-devel amzn 2023 | 1:6.18.16-18.222.amzn2023 | [ALAS2023-2026-1702](https://patchblox.com/security/data/fix/linux/alas2023-2026-1702.md) | May 11, 2026 |
| Linux | kernel6.18-headers amzn 2023 | 1:6.18.16-18.222.amzn2023 | [ALAS2023-2026-1702](https://patchblox.com/security/data/fix/linux/alas2023-2026-1702.md) | May 11, 2026 |
| Linux | kernel6.18-libbpf amzn 2023 | 1:6.18.16-18.222.amzn2023 | [ALAS2023-2026-1702](https://patchblox.com/security/data/fix/linux/alas2023-2026-1702.md) | May 11, 2026 |
| Linux | kernel6.18-libbpf-debuginfo amzn 2023 | 1:6.18.16-18.222.amzn2023 | [ALAS2023-2026-1702](https://patchblox.com/security/data/fix/linux/alas2023-2026-1702.md) | May 11, 2026 |
| Linux | kernel6.18-libbpf-devel amzn 2023 | 1:6.18.16-18.222.amzn2023 | [ALAS2023-2026-1702](https://patchblox.com/security/data/fix/linux/alas2023-2026-1702.md) | May 11, 2026 |
| Linux | kernel6.18-libbpf-static amzn 2023 | 1:6.18.16-18.222.amzn2023 | [ALAS2023-2026-1702](https://patchblox.com/security/data/fix/linux/alas2023-2026-1702.md) | May 11, 2026 |
| Linux | kernel6.18-modules-extra amzn 2023 | 1:6.18.16-18.222.amzn2023 | [ALAS2023-2026-1702](https://patchblox.com/security/data/fix/linux/alas2023-2026-1702.md) | May 11, 2026 |
| Linux | kernel6.18-modules-extra-common amzn 2023 | 1:6.18.16-18.222.amzn2023 | [ALAS2023-2026-1702](https://patchblox.com/security/data/fix/linux/alas2023-2026-1702.md) | May 11, 2026 |
| Linux | kernel6.18-tools amzn 2023 | 1:6.18.16-18.222.amzn2023 | [ALAS2023-2026-1702](https://patchblox.com/security/data/fix/linux/alas2023-2026-1702.md) | May 11, 2026 |
| Linux | kernel6.18-tools-debuginfo amzn 2023 | 1:6.18.16-18.222.amzn2023 | [ALAS2023-2026-1702](https://patchblox.com/security/data/fix/linux/alas2023-2026-1702.md) | May 11, 2026 |
| Linux | kernel6.18-tools-devel amzn 2023 | 1:6.18.16-18.222.amzn2023 | [ALAS2023-2026-1702](https://patchblox.com/security/data/fix/linux/alas2023-2026-1702.md) | May 11, 2026 |
| Linux | linux Debian 13.5 (trixie) | 6.12.85-1 | [DEBIAN-CVE-2026-43244](https://patchblox.com/security/data/fix/linux/debian-cve-2026-43244.md) | May 15, 2026 |
| Linux | linux Debian 14 | 6.19.6-1 | [DEBIAN-CVE-2026-43244](https://patchblox.com/security/data/fix/linux/debian-cve-2026-43244.md) | May 15, 2026 |
| Linux | perf6.12 amzn 2023 | 1:6.12.77-99.140.amzn2023 | [ALAS2023-2026-1543](https://patchblox.com/security/data/fix/linux/alas2023-2026-1543.md) | Apr 7, 2026 |
| Linux | perf6.12-debuginfo amzn 2023 | 1:6.12.77-99.140.amzn2023 | [ALAS2023-2026-1543](https://patchblox.com/security/data/fix/linux/alas2023-2026-1543.md) | Apr 7, 2026 |
| Linux | perf6.18 amzn 2023 | 1:6.18.16-18.222.amzn2023 | [ALAS2023-2026-1702](https://patchblox.com/security/data/fix/linux/alas2023-2026-1702.md) | May 11, 2026 |
| Linux | perf6.18-debuginfo amzn 2023 | 1:6.18.16-18.222.amzn2023 | [ALAS2023-2026-1702](https://patchblox.com/security/data/fix/linux/alas2023-2026-1702.md) | May 11, 2026 |
| Linux | python3-perf6.12 amzn 2023 | 1:6.12.77-99.140.amzn2023 | [ALAS2023-2026-1543](https://patchblox.com/security/data/fix/linux/alas2023-2026-1543.md) | Apr 7, 2026 |
| Linux | python3-perf6.12-debuginfo amzn 2023 | 1:6.12.77-99.140.amzn2023 | [ALAS2023-2026-1543](https://patchblox.com/security/data/fix/linux/alas2023-2026-1543.md) | Apr 7, 2026 |
| Linux | python3-perf6.18 amzn 2023 | 1:6.18.16-18.222.amzn2023 | [ALAS2023-2026-1702](https://patchblox.com/security/data/fix/linux/alas2023-2026-1702.md) | May 11, 2026 |
| Linux | python3-perf6.18-debuginfo amzn 2023 | 1:6.18.16-18.222.amzn2023 | [ALAS2023-2026-1702](https://patchblox.com/security/data/fix/linux/alas2023-2026-1702.md) | May 11, 2026 |

---

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