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CVE-2026-72429
ipv6: ioam: fix type confusion of dst_entry
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem net/ipv6. Debian urgency: unimportant.
Debian does not build this code. The per-release build detail is under "Where it lives" below.
What to do, per Debian release
Debian's own status for CVE-2026-72429 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 | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
IOAM uses a dummy dst_entry(null_dst) to mark that the destination should not be changed after the transformation. This dst is stored in the IOAM lwt state and may be passed to dst_cache_set_ip6(). However, the IPv6 dst cache path eventually calls rt6_get_cookie(), which treats the dst_entry as part of a struct rt6_info. Since the null_dst was embedded directly as a struct dst_entry in struct ioam6_lwt, this resulted in an invalid cast and rt6_get_cookie() reading fields from the wrong object. In practice, the wrong cookie is not used while dst->obsolete is zero, but rt6_get_cookie() may also access per-cpu value when rt->sernum is zero. In this case, rt->sernum aliases ioam6_lwt::cache::reset_ts, which can become zero, making this a potential invalid pointer access. Fix this by embedding a full struct rt6_info for the dummy IPv6 route and passing its dst member to the dst APIs.
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/ipv6/ioam6_iptunnel.c
- What this is
- NETWORKING [IOAM]MAINTAINERS section matched on net/ipv6/ioam6* · Maintained
- Kernel module
- none to look for. The file would have gone into ipv6, and Debian does not compile it into that module, so finding ipv6 in lsmod would say nothing about this CVE.
Check it on the machine
grep -wE 'CONFIG_IPV6|CONFIG_IPV6_IOAM6_LWTUNNEL' /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 does not build this code. In 4 releases below, every kernel flavour Debian publishes has the switch off, so the vulnerable file is compiled into no kernel binary Debian ships.
- bookworm, trixie, forky, sidn
- n
- not enabled on any flavour - this release does not build the code
- Build switches
- CONFIG_IPV6, CONFIG_IPV6_IOAM6_LWTUNNEL
- Reads as
- all on means the file is compiled; any one off means it is not.
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
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.65%, higher than 50.1% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- net/ipv6
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.16 | 6.18.40 | ea24f911ead8 |
| 6.16 | 7.1.5 | 5a3b2ee1e96d |
| 6.16 | 7.2 | 9ed19e11d214 |
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:NAttack vector, network
- The flaw is in ioam6_output() on the IPv6 transmit path (lwtunnel_output→dst_output), reachable when remotely sourced IPv6 packets are forwarded or locally output through an IOAM6 LWT route on internet-facing or LAN routers.
- AC:LAttack complexity, low
- Once IOAM6 LWT inline routes exist, an attacker can reliably trigger the null_dst dst_cache_set_ip6() path by sending IPv6 traffic that misses the per-CPU dst cache, without races or uncontrollable memory layout.
- PR:NPrivileges required, none
- Exploitation requires only the ability to send IPv6 packets; IOAM6 LWT route and namespace setup needs CAP_NET_ADMIN on the victim but is an operator deployment prerequisite, not attacker privilege.
- UI:NUser interaction, none
- No victim user action is required beyond normal network operation; crafted or high-volume IPv6 packets alone drive the vulnerable output path.
- S:UScope, unchanged
- Impact is kernel memory corruption and crash within the host kernel; it does not cross VM, container, or IOMMU security boundaries.
- C:HConfidentiality impact, high
- Type confusion makes rt6_get_cookie() treat ioam6_lwt fields as rt6_info members and chase a misinterpreted fib6_info pointer via fib6_get_cookie_safe(), enabling out-of-bounds kernel memory reads.
- I:HIntegrity impact, high
- Casting a standalone dst_entry to rt6_info is type confusion that corrupts pointer interpretation and dst_cache cookie state, a class exploitable toward arbitrary kernel writes or control-flow hijack.
- A:HAvailability impact, high
- The confused rt6_info layout can dereference invalid fib6_info/fib6_node pointers, causing kernel oops or panic; memory corruption in the networking fast path also risks host-wide denial of service.