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CVE-2026-74438
crypto: sun4i-ss - Remove insecure and unused rng_alg
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem arch/arm. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-74438 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 | fixed | 6.1.180-1 | Update the kernel and reboot. Fixed in 6.1.180-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.100-1 | Update the kernel and reboot. Fixed in 6.12.100-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Remove sun4i_ss_rng, as it is insecure and unused: - It has multiple vulnerabilities. sun4i_ss_prng_seed() is missing locking and has a buffer overflow. sun4i_ss_prng_generate() fails to fill the entire buffer with cryptographic random bytes, because it rounds the destination length down and also doesn't actually wait for the hardware to be ready before pulling bytes from it. - No user of this code is known. It's usable only theoretically via the "rng" algorithm type of AF_ALG. But userspace actually just uses the actual Linux RNG (/dev/random etc) instead. And rng_algs don't contribute entropy to the actual Linux RNG either. (This may have been confused with hwrng, which does contribute entropy.) The sun4i_ss_prng_seed() buffer overflow was reported by Tianchu Chen and discovered by Atuin - Automated Vulnerability Discovery Engine There's no point in fixing all these vulnerabilities individually when this is unused code, so let's just remove it.
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.
arch/arm/configs/sunxi_defconfig
drivers/crypto/allwinner/Kconfig
drivers/crypto/allwinner/sun4i-ss/Makefile
drivers/crypto/allwinner/sun4i-ss/sun4i-ss-core.c
drivers/crypto/allwinner/sun4i-ss/sun4i-ss-prng.c
drivers/crypto/allwinner/sun4i-ss/sun4i-ss.h
- What this is
- ARM PORTMAINTAINERS section matched on arch/arm/ · linux-arm-kernel@lists.infradead.org · Odd Fixes
- Kernel module
- sun4i_ss
Check it on the machine
grep -wE 'CONFIG_CRYPTO|CONFIG_CRYPTO_DEV_ALLWINNER|CONFIG_CRYPTO_DEV_SUN4I_SS' /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 sun4i_ssPrints 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.
- bookwormMnot built on amd64/amd64, amd64/cloud-amd64, amd64/rt/amd64, arm64/arm64, arm64/cloud-arm64, arm64/rt/arm64, i386/686, i386/686-pae, i386/rt/686-pae, ppc64el/powerpc64le
- trixieMnot built on amd64/amd64, amd64/cloud-amd64, amd64/rt/amd64, arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, arm64/rt/arm64, armel/rpi, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64, s390x/s390x
- forky, sidMnot built on amd64/amd64, amd64/cloud-amd64, amd64/rt-amd64, arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, arm64/rt-arm64, loong64/loong64, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64, s390x/s390x
- M
- a module where it is built at all; some flavours do not build it
- Build switches
- CONFIG_CRYPTO, CONFIG_CRYPTO_DEV_ALLWINNER, CONFIG_CRYPTO_DEV_SUN4I_SS
- 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
- 2026-08-15 (2 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
- 0.19%, higher than 8.1% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- arch/arm
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.14 | 5.15.212 | 2eafecaba1b4 |
| 4.14 | 6.1.178 | ee2458f81887 |
| 4.14 | 6.6.145 | 306ded31bfa0 |
| 4.14 | 6.12.97 | e4b7b9819811 |
| 4.14 | 6.18.40 | c401492e01c7 |
| 4.14 | 7.1.5 | 9c8086d95111 |
| 4.14 | 7.2 | b2c41fa9dd8f |
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 sun4i_ss_prng_seed() is reached only through the AF_ALG userspace crypto API (socket/bind/setsockopt ALG_SET_KEY/accept/recvmsg), which is a local syscall interface with no network-facing handler exposing this Allwinner PRNG.
- AC:LAttack complexity, low
- On affected Allwinner systems with CONFIG_CRYPTO_DEV_SUN4I_SS_PRNG enabled, an attacker deterministically triggers the overflow by passing a seed longer than the 24-byte ss->seed buffer via ALG_SET_KEY; no race or external state is required, and concurrent seed/generate races are attacker-controlled.
- PR:LPrivileges required, low
- AF_ALG RNG sockets are available to unprivileged local users without capabilities; only ALG_SET_DRBG_ENTROPY requires CAP_SYS_ADMIN. No root or namespace-spawned admin capability is needed to bind to sun4i_ss_rng and invoke the seed path.
- UI:NUser interaction, none
- Exploitation requires only the attacker's own PF_ALG socket operations; no victim must mount devices, open files, or perform any interactive action.
- S:UScope, unchanged
- The heap buffer overflow corrupts kernel memory within the sun4i-ss driver's context structure and adjacent slab objects, staying within kernel privilege domain; it does not cross VM, IOMMU, or sandbox boundaries.
- C:HConfidentiality impact, high
- memcpy() with attacker-controlled slen past the 24-byte ss->seed array overwrites dbgfs_dir/dbgfs_stats pointers and subsequent kernel heap data, giving an out-of-bounds write that can be leveraged for arbitrary kernel memory disclosure.
- I:HIntegrity impact, high
- The unchecked slen in sun4i_ss_prng_seed() is a kernel heap buffer overflow past ss->seed[6], corrupting adjacent kernel objects and enabling controlled overwrite primitives suitable for privilege escalation or code execution.
- A:HAvailability impact, high
- Heap corruption from the seed buffer overflow or concurrent unlocked seed()/locked generate() races can cause kernel oops/panic or hang, and the overflow is repeatable on demand via ALG_SET_KEY without authentication.