CVE-2026-43244In 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 mes…

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

CVSS

5.5 MEDIUM (v3.1, NVD)CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Weakness (CWE)

CWE-401

Known exploited

Not in CISA's KEV catalog

EPSS (exploitation in the next 30 days)

Not loaded for this CVE

Assigned by

Not given

NVD analysis

Analyzed

Record last updated

Jun 17, 2026

First seen by InfoSec Signals

Oct 9, 2026

The CVE record on cve.org · NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.