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CVE-2026-53228
ipv6: sit: reload inner IPv6 header after GSO offloads
Published 2026-06-25 (4 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-2026-53228 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-4665-1 · 2026-07-03 · text | 6.1.176-1 | Update the kernel and reboot. DLA-4665-1 shipped the fix on 2026-07-03, in 6.1.176-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.94-1 | Update the kernel and reboot. Fixed in 6.12.94-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.0.13-1 | Update the kernel and reboot. Fixed in 7.0.13-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.13-1 | Update the kernel and reboot. Fixed in 7.0.13-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
ipip6_tunnel_xmit() caches the inner IPv6 header pointer at function entry and continues using it after iptunnel_handle_offloads(). For GSO skbs, iptunnel_handle_offloads() calls skb_header_unclone(). When the skb header is cloned, skb_header_unclone() can call pskb_expand_head(), which may move the skb head. The pskb_expand_head() contract requires pointers into the skb header to be reloaded after the call. If the later skb_realloc_headroom() branch is not taken, SIT uses the stale iph6 pointer to read the inner hop limit and DS field. That can read from a freed skb head after the old head's remaining clone is released. Reload iph6 after the offload helper succeeds and before subsequent reads from the inner IPv6 header. Keep the existing reload after skb_realloc_headroom(), since that branch can also replace the skb.
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/sit.c
- What this is
- NETWORKING [GENERAL]MAINTAINERS section matched on net/ · netdev@vger.kernel.org · Maintained
- Kernel module
- sit
Check it on the machine
grep -w CONFIG_IPV6_SIT /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 sitPrints 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, sidm
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switch
- CONFIG_IPV6_SIT
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
- 2026-06-25 (4 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
- 0.58%, higher than 46.3% 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 |
|---|---|---|
| 3.18 | 5.10.259 | fddd41445a05 |
| 3.18 | 5.15.210 | 1132e5edc286 |
| 3.18 | 6.1.176 | 9c67b44edb35 |
| 3.18 | 6.6.143 | 0bfa7bba1f41 |
| 3.18 | 6.12.94 | 59f80c919713 |
| 3.18 | 6.18.36 | 2fa49b2715e1 |
| 3.18 | 7.0.13 | cb658c2f5f79 |
| 3.18 | 7.1 | f0e42f0c4337 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4671-1 | 2026-07-05 | bullseye 6.1.176-1~deb11u1 | tracker |
| DLA-4665-1 | 2026-07-03 | bookworm 6.1.176-1 | tracker |
| DLA-4664-1 | 2026-07-03 | bullseye 5.10.259-1 | 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 vulnerable SIT transmit path can be reached by network-triggered IPv6 traffic in a reasonable deployment where a public service or router sends large TCP/GSO packets through a configured SIT tunnel.
- AC:LAttack complexity, low
- There is no race or fragile timing requirement; GSO and header-cloned TCP skbs are normal for large TCP transmissions, and the attacker can repeatedly trigger them with network traffic.
- PR:NPrivileges required, none
- In the network-triggered scenario, the attacker does not need local privileges or authentication; the required SIT configuration is an environmental precondition on the victim.
- UI:NUser interaction, none
- No victim user action is required beyond the system processing network traffic through the configured SIT tunnel.
- S:UScope, unchanged
- The impact remains within the kernel and its networking security authority, with no VM, IOMMU, or separate security-scope boundary crossed.
- C:HConfidentiality impact, high
- The stale inner IPv6 header pointer can read from freed skb head memory after `skb_header_unclone()`/`pskb_expand_head()`, making this a kernel use-after-free read. Per kernel CVSS guidance, use-after-free conditions are scored with high confidentiality impact.
- I:HIntegrity impact, high
- Although the immediate stale access feeds header fields, it is a kernel use-after-free in attacker-triggerable networking memory, and kernel UAFs are treated as potentially exploitable for heap manipulation and integrity compromise.
- A:HAvailability impact, high
- Use-after-free in the kernel networking transmit path can lead to oops, panic, or repeated crash conditions, especially under memory debugging or unfavorable heap reuse.