CVE-2026-31778

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.

Weakness

The product reads data past the end, or before the beginning, of the intended buffer.

Affected Software

Potential Mitigations

• Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
• When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
• Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
• To reduce the likelihood of introducing an out-of-bounds read, ensure that you validate and ensure correct calculations for any length argument, buffer size calculation, or offset. Be especially careful of relying on a sentinel (i.e. special character such as NUL) in untrusted inputs.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/540.html

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