CVE-2026-89720

Summary

In the Linux kernel, the following vulnerability has been resolved:

ubifs: fix out-of-bounds read in signature length check

ubifs_sb_verify_signature() bounds the on-disk ubifs_sig_node->len field before handing the signature payload to verify_pkcs7_signature(), but the check has the wrong sign:

if (le32_to_cpu(signode->len) > snod->len + sizeof(struct ubifs_sig_node))

The signature bytes start sizeof(struct ubifs_sig_node) (UBIFS_SIG_NODE_SZ, 64 bytes) into the node, so the payload is at most

snod->len - sizeof(struct ubifs_sig_node)

bytes long. Adding the header size instead of subtracting it accepts a declared length up to 2 * UBIFS_SIG_NODE_SZ larger than the node actually holds – past the end of c->sbuf, which is vmalloc(c->leb_size). verify_pkcs7_signature() -> pkcs7_parse_message() -> asn1_ber_decoder() is then handed that inflated length and reads beyond the allocation while walking the DER headers. The node length comes straight from the mounted image, so a crafted signed UBIFS image reaches this via ubifs_read_superblock() before the signature is cryptographically checked.

snod->len is guaranteed to be >= UBIFS_SIG_NODE_SZ by the node scanner (c->ranges[UBIFS_SIG_NODE].min_len == UBIFS_SIG_NODE_SZ), so the corrected subtraction cannot underflow. Legitimately signed images are unaffected: a correct superblock never declares a signature longer than the node it is embedded in.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/f76b79d6e42af20682495bccd22f72c7164b0018
• https://git.kernel.org/stable/c/a1dc246f98bb94233effa4fa3ec7bf84700bb7d1
• https://git.kernel.org/stable/c/83e1aa9f5f906c9b1f4949d0521f0f950a159d96
• https://git.kernel.org/stable/c/95d27c1708bb6e8823c8e7c623f9abc2a91bf4bf

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