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CVE-2026-53366
ipv4: account for fraggap on the paged allocation path
Published 2026-07-16 (3 months ago) by the Linux kernel CNA. Subsystem net/ipv4. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-53366 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-4688-1 · 2026-07-18 · text | 6.1.177-1 | Update the kernel and reboot. DLA-4688-1 shipped the fix on 2026-07-18, in 6.1.177-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.95-1 | Update the kernel and reboot. Fixed in 6.12.95-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.3-1 | Update the kernel and reboot. Fixed in 7.1.3-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.3-1 | Update the kernel and reboot. Fixed in 7.1.3-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
In __ip_append_data(), when the paged-allocation branch is taken, alloclen and pagedlen are computed as alloclen = fragheaderlen + transhdrlen; pagedlen = datalen - transhdrlen; datalen already includes fraggap, but the fraggap bytes carried over from the previous skb are copied into the new skb's linear area at offset transhdrlen by the subsequent skb_copy_and_csum_bits(). The linear area is therefore undersized by fraggap bytes while pagedlen is overstated by the same amount. The non-paged branch sets alloclen to fraglen, which already accounts for fraggap because datalen does. Bring the paged branch in line by adding fraggap to alloclen and subtracting it from pagedlen. After this adjustment, copy no longer collapses to -fraggap on the paged path, so remove the stale comment describing that old arithmetic.
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/ip_output.c
- What this is
- NETWORKING [IPv4/IPv6]MAINTAINERS section matched on net/ipv4/ip* · 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
- 2026-07-16 (3 months 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
- 0.17%, higher than 6.1% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- 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 |
|---|---|---|
| 6.0 | 6.1.178 | 5c6375bced61 |
| 6.0 | 6.6.144 | ce494707a9c0 |
| 6.0 | 6.12.95 | a9c24eda24bd |
| 6.0 | 6.18.38 | 77798d7be6ef |
| 6.0 | 7.1.3 | c04d9ece23de |
| 6.0 | 7.2 | eca856950f7c |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4700-1 | 2026-07-26 | bullseye 6.1.177-1~deb11u1 | tracker |
| DLA-4688-1 | 2026-07-18 | bookworm 6.1.177-1 | 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 vulnerable code is reached while a local process constructs outgoing IPv4 UDP/raw/ping datagrams through sendmsg/splice/sendfile-style socket paths. I did not find a defensible received-packet or unauthenticated remote path that supplies the required cork/MSG_MORE-style fraggap conditions.
- AC:LAttack complexity, low
- The attacker can choose UDP socket options/flags, payload sizes, corking/MSG_MORE behavior, and splice/zerocopy-style paged sends to reach the fraggap paged-allocation path. There is no race or external timing condition required.
- PR:LPrivileges required, low
- A normal unprivileged local user can create IPv4 UDP sockets and use UDP_CORK/MSG_MORE/splice or related paged send paths; raw sockets are CAP_NET_RAW-gated but are not needed for the strongest local trigger. This is therefore basic local user privilege, not real administrator privilege.
- UI:NUser interaction, none
- No victim interaction is required once the attacker can run the local send/splice sequence. The vulnerable skb construction happens synchronously in the attacker-driven socket send path.
- S:UScope, unchanged
- The impact is within the same kernel security authority as the vulnerable IPv4 networking code. This is not a VM escape, IOMMU bypass, or cross-authority boundary violation.
- C:HConfidentiality impact, high
- The bug under-allocates/accounting for the linear skb area and can copy attacker-controlled fraggap bytes past skb->end into trailing skb_shared_info metadata. Kernel memory corruption of this kind is reasonably capable of being developed into information disclosure, so the higher severity confidentiality value is appropriate.
- I:HIntegrity impact, high
- The copied fraggap bytes corrupt kernel skb metadata past the intended buffer boundary. This is an out-of-bounds write in kernel heap/networking structures and is scored as high integrity impact.
- A:HAvailability impact, high
- The corrupted skb metadata can crash or destabilize the kernel networking stack, and related negative-copy accounting can also produce severe send-path failure behavior. Kernel crash or oops potential is high availability impact.