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CVE-2026-74562
nexthop: take nh->lock for f6i_list walks in replace check and notify
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem net/ipv4. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-74562 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| Debian 14forky | fixed | 7.1.8-1 | Update the kernel and reboot. Fixed in 7.1.8-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.8-1 | Update the kernel and reboot. Fixed in 7.1.8-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
fib6_check_nh_list() and __nexthop_replace_notify() walk nh->f6i_list during an RTNL-serialized nexthop replace without holding nh->lock. IPv6 RTM_NEWROUTE/RTM_DELROUTE run without RTNL and mutate that list under nh->lock (fib6_add_rt2node_nh(), fib6_purge_rt()), so both walks race a concurrent route delete that unlinks and frees a fib6_info: BUG: KASAN: slab-use-after-free in rt6_fill_node.isra.0 (net/ipv6/route.c:5799) Read of size 4 at addr ffff888014607e64 by task exploit/143 rt6_fill_node.isra.0 (net/ipv6/route.c:5799) fib6_rt_update (net/ipv6/route.c:6412) __nexthop_replace_notify (net/ipv4/nexthop.c:2542) rtm_new_nexthop (net/ipv4/nexthop.c:2554) rtnetlink_rcv_msg (net/core/rtnetlink.c:7076) BUG: KASAN: slab-use-after-free in fib6_check_nh_list (net/ipv4/nexthop.c:1605) Read of size 8 at addr ffff888014a7d068 by task exploit/142 fib6_check_nh_list (net/ipv4/nexthop.c:1605) rtm_new_nexthop (net/ipv4/nexthop.c:2575) rtnetlink_rcv_msg (net/core/rtnetlink.c:7076) Both walks only read the entries and take no tb6_lock, so protect them with nh->lock; fib6_rt_update() uses gfp_any(), which returns GFP_ATOMIC under the lock.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
net/ipv4/nexthop.c
- What this is
- NETWORKING [IPv4/IPv6]MAINTAINERS section matched on net/ipv4/nexthop.c · netdev@vger.kernel.org · Maintained
Check it on the machine
grep -w CONFIG_INET /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
Show whether Debian builds this, per release
Debian builds this code. Every release below compiles the affected file into the kernels it ships.
- bookworm, trixie, forky, sidy
- y
- built into the kernel image on every flavour - only a patch removes it
- Build switch
- CONFIG_INET
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-08-15 (2 months ago)source
- CVSS
- 8.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.17%, higher than 5.8% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- net/ipv4
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.16 | 6.18.57 | 4b296d176580 |
| 6.16 | 7.1.8 | bb2b072c619c |
| 6.16 | 7.2 | 072cd1f21819 |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- The bug is reached only via local RTNETLINK messages (RTM_NEWNEXTHOP replace and concurrent RTM_NEWROUTE/RTM_DELROUTE) sent on AF_NETLINK sockets, not by processing remote network packets.
- AC:LAttack complexity, low
- An attacker can reliably trigger the race by running concurrent netlink threads that replace a nexthop while deleting IPv6 routes bound to it; both sides of the race are attacker-controlled, as demonstrated by the reported KASAN reproducers.
- PR:LPrivileges required, low
- All vulnerable rtnetlink handlers require CAP_NET_ADMIN via netlink_net_capable(), which unprivileged local users can obtain inside a user/network namespace (unshare -Urn), not only real init-namespace root.
- UI:NUser interaction, none
- Exploitation requires no victim interaction beyond the attacker issuing coordinated netlink configuration commands from local processes.
- S:CScope, changed
- A successful UAF from CAP_NET_ADMIN inside a user/network namespace can corrupt host kernel memory and escape the container sandbox to compromise the host system.
- C:HConfidentiality impact, high
- The race performs use-after-free reads of freed fib6_info objects (e.g., fib6_src and fib6_flags in fib6_check_nh_list and rt6_fill_node), enabling arbitrary kernel memory disclosure via heap reuse.
- I:HIntegrity impact, high
- Slab UAF on fib6_info during nexthop replace notification can be leveraged with heap spraying for arbitrary kernel writes and local privilege escalation to host root.
- A:HAvailability impact, high
- The bug provably causes slab-use-after-free kernel oops (KASAN) during route notification and can panic or hang the system when triggered repeatedly.