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CVE-2026-31630
rxrpc: proc: size address buffers for %pISpc output
Published 2026-04-24 (6 months ago) by the Linux kernel CNA. Subsystem net/rxrpc. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-31630 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 | vulnerable | 6.12.113-1 | No fix published anywhere yet, neither in Debian nor upstream for the series trixie tracks. Watch the Debian tracker page for this CVE. Advisories for trixie have historically landed a median of 11 days after publication. |
| Debian 14forky | fixed | 6.19.13-1 | Update the kernel and reboot. Fixed in 6.19.13-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 6.19.13-1 | Update the kernel and reboot. Fixed in 6.19.13-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
The AF_RXRPC procfs helpers format local and remote socket addresses into fixed 50-byte stack buffers with "%pISpc". That is too small for the longest current-tree IPv6-with-port form the formatter can produce. In lib/vsprintf.c, the compressed IPv6 path uses a dotted-quad tail not only for v4mapped addresses, but also for ISATAP addresses via ipv6_addr_is_isatap(). As a result, a case such as [ffff:ffff:ffff:ffff:0:5efe:255.255.255.255]:65535 is possible with the current formatter. That is 50 visible characters, so 51 bytes including the trailing NUL, which does not fit in the existing char[50] buffers used by net/rxrpc/proc.c. Size the buffers from the formatter's maximum textual form and switch the call sites to scnprintf(). Changes since v1: - correct the changelog to cite the actual maximum current-tree case explicitly - frame the proof around the ISATAP formatting path instead of the earlier mapped-v4 example
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/rxrpc/proc.c
- What this is
- RXRPC SOCKETS (AF_RXRPC)MAINTAINERS section matched on net/rxrpc/ · linux-afs@lists.infradead.org · Supported
- Kernel module
- rxrpc
Check it on the machine
grep -wE 'CONFIG_AF_RXRPC|CONFIG_PROC_FS' /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 rxrpcPrints 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, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.
- bookworm, trixie, forky, sidMnot built on amd64/cloud-amd64, arm64/cloud-arm64
- M
- a module where it is built at all; some flavours do not build it
- Build switches
- CONFIG_AF_RXRPC, CONFIG_PROC_FS
- 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
- 2026-04-24 (6 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
- 0.18%, higher than 6.7% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/rxrpc
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.9 | 5.10.258 | 386c86412608 |
| 4.9 | 5.15.209 | 235b2115de89 |
| 4.9 | 6.1.175 | 625af53a1564 |
| 4.9 | 6.18.23 | db297c78ce53 |
| 4.9 | 6.19.13 | 10ebed83f9f6 |
| 4.9 | 7.0 | a44ce6aa2efb |
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:LAttack vector, local
- The overflowing sprintf is executed when a local process reads the world-readable RXRPC procfs seq files under /proc/net/rxrpc. A remote RXRPC peer can influence stored addresses on a listening service, but cannot directly invoke the proc show path without a local proc read.
- AC:LAttack complexity, low
- No race or hard-to-control timing is required; an attacker can create or cause an RXRPC IPv6 peer/address with the maximal ISATAP-style textual form and read the proc entry. The overflow condition is deterministic once such an address is present.
- PR:LPrivileges required, low
- The proc entries are created mode 0444 and RXRPC socket creation/sendmsg paths do not impose a capability check, so a basic unprivileged local user can reach the vulnerable show functions. This does not require real root or init-namespace administrative privileges.
- UI:NUser interaction, none
- The attacker can trigger the vulnerable formatting by reading the proc file themselves. No separate victim action is required.
- S:UScope, unchanged
- The bug corrupts kernel memory within the same kernel security authority. It is not a VM escape, IOMMU bypass, or cross-scope boundary violation.
- C:HConfidentiality impact, high
- The bug is kernel stack memory corruption from an out-of-bounds write in attacker-reachable code. Following the higher-severity rule for memory corruption, successful exploitation could compromise kernel confidentiality.
- I:HIntegrity impact, high
- The vulnerable sprintf writes past a fixed stack buffer, giving an out-of-bounds kernel stack write. Under the required scoring guidance, out-of-bounds writes are treated as high integrity impact due to potential control-flow or kernel state corruption.
- A:HAvailability impact, high
- Even if not shaped into code execution, the stack corruption can produce an oops, panic, or other kernel crash. The attacker can retrigger it repeatedly by reading the affected proc entries while the crafted address object exists.