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CVE-2026-74597
ip6_tunnel: clear skb2->cb[] in ip6ip6_err()
Published 2026-08-22 (2 months 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-2026-74597 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-4777-1 · 2026-09-08 · text | 6.1.187-1 | Update the kernel and reboot. DLA-4777-1 shipped the fix on 2026-09-08, in 6.1.187-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6466-1 · 2026-08-25 · text | 6.12.105-1 | Update the kernel and reboot. DSA-6466-1 shipped the fix on 2026-08-25, in 6.12.105-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4788-1 · 2026-09-19 · text | 6.12.107-1~deb12u1 | Update the kernel and reboot. DLA-4788-1 shipped the fix on 2026-09-19, in 6.12.107-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
ip6ip6_err() clones an outer IPv6 ICMP error skb, pulls it to the quoted inner IPv6 packet, and then passes the clone to icmpv6_send(). The clone still carries the outer packet's inet6_skb_parm in skb->cb. If the outer packet had a Home Address Option, IP6CB(skb2)->dsthao remains non-zero after skb_pull(). icmpv6_send() later calls mip6_addr_swap(), which uses that stale dsthao offset against the quoted inner packet. A malformed inner destination-options header can then make the HAO lookup and address swap run past the end of the quoted packet and corrupt skb_shared_info. Clear skb2->cb[] before pulling the quoted inner IPv6 packet so the reply path does not reuse metadata left by the outer IPv6 stack.
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/ip6_tunnel.c
- What this is
- NETWORKING [IPv4/IPv6]MAINTAINERS section matched on net/ipv6/ip* · netdev@vger.kernel.org · Maintained
- Kernel module
- ip6_tunnel
Check it on the machine
grep -w CONFIG_IPV6_TUNNEL /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.
lsmod | grep -w ip6_tunnelPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this as a loadable module. Every release below compiles it as a module on every flavour, so whether the code is in the running kernel depends on whether that module is loaded.
- bookworm, trixie, forky, sid, bookworm · linux-6.12m
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switch
- CONFIG_IPV6_TUNNEL
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
- 2026-08-22 (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
- 0.54%, higher than 44.4% 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 |
|---|---|---|
| 2.6.22 | 5.10.265 | 44fe898df302 |
| 2.6.22 | 5.15.216 | 0dadb0620ab6 |
| 2.6.22 | 6.1.183 | b6816536a299 |
| 2.6.22 | 6.6.152 | 64e41736a26f |
| 2.6.22 | 6.12.104 | 484134e1eb07 |
| 2.6.22 | 6.18.45 | 4eb15c465337 |
| 2.6.22 | 7.1.9 | fbf40faa0414 |
| 2.6.22 | 7.2 | f803c086399d |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4788-1 | 2026-09-19 | bookworm 6.12.107-1~deb12u1 | tracker |
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | tracker |
| DSA-6466-1 | 2026-08-25 | trixie 6.12.105-1 | 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:NAttack vector, network
- The bug is reached when a remote peer sends a forged ICMPv6 error whose quoted payload is an IPv6-in-IPv6 tunnel datagram; processing follows the normal IPv6 receive path (ipv6_rcv -> icmpv6_notify -> tunnel6_err -> ip6ip6_err) with no local access required.
- AC:LAttack complexity, low
- The attacker controls the carrier IPv6 Home Address Option, quoted tunnel/inner headers, and ICMP error type; once an ip6tnl endpoint exists (normal for this subsystem), triggering the stale-dsthao path is reliable and needs no races or victim interaction.
- PR:NPrivileges required, none
- No authentication or capabilities are required on the target; unprivileged remote senders can deliver crafted ICMPv6 errors that the kernel processes on the standard pre-auth receive path (INET6_PROTO_NOPOLICY).
- UI:NUser interaction, none
- Exploitation requires only delivering a malicious network packet; no victim must open files, click links, or perform any other action.
- S:UScope, unchanged
- Impact is in-kernel memory corruption on the receiving host within the same security authority; it does not by itself cross VM, container, or IOMMU boundaries.
- C:HConfidentiality impact, high
- With CONFIG_IPV6_MIP6, mip6_addr_swap() uses the stale dsthao offset to scan the quoted inner packet and can read attacker-controlled bytes past the skb tail while resolving a fake HAO TLV before swapping addresses.
- I:HIntegrity impact, high
- The resulting 16-byte swap(iph->saddr, hao->addr) can write beyond the quoted packet into skb_shared_info, giving attacker-influenced heap corruption suitable for further control-flow or data manipulation.
- A:HAvailability impact, high
- Corrupting skb_shared_info from the network input path can cause kernel oops/panic or otherwise deny service on IPv6 tunnel endpoints, and the condition is repeatable with crafted packets.