CVE-2026-43139 xfrm6: fix uninitialized saddr in xfrm6_get_saddr()
An attacker can read uninitialized kernel memory via IPv6 XFRM lookups, potentially exposing sensitive data.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-43139?
CVE-2026-43139 is a high-severity vulnerability in Linux kernel, published on 6 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-43139?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-43139?
Apply the vendor's patch.
Is CVE-2026-43139 being exploited?
There is no known exploitation of CVE-2026-43139 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-43139, DEBIAN-CVE-2026-43139, GHSA-hr53-gf94-w7mp, ROOT-OS-DEBIAN-11-CVE-2026-43139, ROOT-OS-UBUNTU-2204-CVE-2026-43139, ROOT-OS-UBUNTU-2404-CVE-2026-43139 and 1 more.