CVE-2026-31778

Description

In the Linux kernel, the following vulnerability has been resolved: ALSA: caiaq: fix stack out-of-bounds read in init_card The loop creates a whitespace-stripped copy of the card shortname where `len < sizeof(card->id)` is used for the bounds check. Since sizeof(card->id) is 16 and the local id buffer is also 16 bytes, writing 16 non-space characters fills the entire buffer, overwriting the terminating nullbyte. When this non-null-terminated string is later passed to snd_card_set_id() -> copy_valid_id_string(), the function scans forward with `while (*nid && ...)` and reads past the end of the stack buffer, reading the contents of the stack. A USB device with a product name containing many non-ASCII, non-space characters (e.g. multibyte UTF-8) will reliably trigger this as follows: BUG: KASAN: stack-out-of-bounds in copy_valid_id_string sound/core/init.c:696 [inline] BUG: KASAN: stack-out-of-bounds in snd_card_set_id_no_lock+0x698/0x74c sound/core/init.c:718 The off-by-one has been present since commit bafeee5b1f8d ("ALSA: snd_usb_caiaq: give better shortname") from June 2009 (v2.6.31-rc1), which first introduced this whitespace-stripping loop. The original code never accounted for the null terminator when bounding the copy. Fix this by changing the loop bound to `sizeof(card->id) - 1`, ensuring at least one byte remains as the null terminator.

Predictions

Heuristic predictions, AS-IS, for prioritization only.

Mitigations

References

• https://git.kernel.org/stable/c/02d9c5b0b5553a391448b6d655262bd829f90234
• https://git.kernel.org/stable/c/3178b62e2e31bab39f63d4c8e54bf4ee0a425627
• https://git.kernel.org/stable/c/3afa2e67f3523a980a2f90fd63c22322ac2b9ce0
• https://git.kernel.org/stable/c/3f7f8bae0d52cbd07ab04b76b6aac89ef98ee9f6
• https://git.kernel.org/stable/c/45424e871abf2a152e247a9cff78359f18dd95c0
• https://git.kernel.org/stable/c/66194c2575a4f567577ae70b1d7561163ce791a6
• https://git.kernel.org/stable/c/7594a6464873d90fd229e5b94cdd3b92c9feabed
• https://git.kernel.org/stable/c/a82c1bce2d1299dd3c686a8fe48cf75b79a403c7
• https://www.suse.com/security/cve/CVE-2026-31778.html
• https://security-tracker.debian.org/tracker/CVE-2026-31778

CWEs

CWE-125