Look up another CVE · open CVE-2026-98241 in the interactive tracker
CVE-2026-98241
ipv6: xfrm: use full sockets in local error paths
Published 2026-10-06 (13 days ago) by the Linux kernel CNA. Subsystem net/ipv6. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-98241 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 | fixedDLA-4841-1 · 2026-10-17 · text | 6.1.190-1 | Update the kernel and reboot. DLA-4841-1 shipped the fix on 2026-10-17, in 6.1.190-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6568-1 · 2026-10-16 · text | 6.12.113-1 | Update the kernel and reboot. DSA-6568-1 shipped the fix on 2026-10-16, in 6.12.113-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.2.8-1 | Update the kernel and reboot. Fixed in 7.2.8-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.8-1 | Update the kernel and reboot. Fixed in 7.2.8-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
xfrm6_local_rxpmtu() and xfrm6_local_error() dereference skb->sk as if it always pointed at a full IPv6 socket. That is not guaranteed. TCP SYN-ACK skbs can be owned by a TCP_NEW_SYN_RECV request_sock while the output path itself is driven by the full listener. If rerouting selects an IPv6 XFRM tunnel route with a lower MTU, the local PMTU/error handling path can reach these callbacks with that mini-socket still attached to the skb. The callbacks then miscast the request socket as a full inet/IPv6 socket and can read beyond the request_sock allocation when they access inet_sock or ipv6_pinfo state. Resolve the owner with skb_to_full_sk() in both callbacks and bail out when no full socket is attached. This matches the surrounding XFRM IPv6 PMTU/error logic, which already reasons about full sockets with skb_to_full_sk().
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/xfrm6_output.c
- What this is
- NETWORKING [IPSEC]MAINTAINERS section matched on net/ipv6/xfrm* · netdev@vger.kernel.org · Maintained
Check it on the machine
grep -wE 'CONFIG_IPV6|CONFIG_XFRM' /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 switches
- CONFIG_IPV6, CONFIG_XFRM
- 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
- 2026-10-06 (13 days ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.14%, higher than 2.9% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- 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 |
|---|---|---|
| 3.2 | 5.10.271 | b1a88633c36d |
| 3.2 | 5.15.222 | 904a0e827d0d |
| 3.2 | 6.1.189 | 675919e08ce2 |
| 3.2 | 6.6.158 | 60459c670329 |
| 3.2 | 6.12.112 | ca3d68c32134 |
| 3.2 | 6.18.54 | 4c030a0400eb |
| 3.2 | 7.2.8 | c21f3f7fbfed |
| 3.2 | 7.3 | 6973a21ee73c |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4841-1 | 2026-10-17 | bookworm 6.1.190-1 | tracker |
| DSA-6568-1 | 2026-10-16 | trixie 6.12.113-1 | tracker |
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 fixed xfrm6_local_error() is reached via __xfrm6_output() -> xfrm_local_error() only if a rerouted SYN-ACK exceeds an xfrm tunnel MTU below ~100 bytes; that needs local xfrm/route/netfilter setup. A remote SYN carries no malformed data and can't create this state (IPv4 PMTU floor is 552, xfrm6_tunnel_check_size clamps to 1280).
- AC:LAttack complexity, low
- The attacker builds every precondition: an IPv6-in-IPv4 tunnel-mode xfrm SA/policy, a tiny outer MTU, a LOCAL_OUT reroute, and a TCP listener they connect to. Each SYN deterministically sends a SYN-ACK owned by a TCP_NEW_SYN_RECV request_sock down the !ignore_df && toobig branch.
- PR:LPrivileges required, low
- The needed XFRM_MSG_NEWSA/NEWPOLICY, nftables rules and link MTU changes only need CAP_NET_ADMIN in the netns, which an unprivileged user gets via unshare -Urn; the listener and connect() are ordinary syscalls.
- UI:NUser interaction, none
- The attacker sets up the namespace and drives the handshake that emits the SYN-ACK themselves; no other user has to do anything.
- S:UScope, unchanged
- The out-of-bounds access corrupts kernel heap memory in the same kernel that enforces the attacker's namespace; no hypervisor or IOMMU boundary is crossed.
- C:HConfidentiality impact, high
- xfrm6_local_error() passes the request_sock to ipv6_local_error() as a full IPv6 socket; inet6_test_bit(RECVERR6) reads inet_flags past the end of the tcp6_request_sock allocation, into the next slab object, and the rest of the path keeps reading socket fields out of bounds.
- I:HIntegrity impact, high
- If the out-of-bounds RECVERR6 bit is set, sock_queue_err_skb() does atomic_add on an OOB sk_rmem_alloc, links an skb into an OOB sk_error_queue list and calls the OOB sk_error_report pointer: heap writes plus control-flow hijack if the attacker grooms the adjacent object.
- A:HAvailability impact, high
- Treating neighbouring slab memory as sk_error_queue and sk_error_report gives list corruption or a wild indirect call, crashing the kernel; the attacker can repeat it with each SYN.