CVE-2026-89720
HighCVSS 7.7Exploitation Probability (EPSS)
Low risk8th percentile - higher than 8% of all known CVEs
Summary
In the Linux kernel, ubifs_sb_verify_signature() bounds the on-disk ubifs_sig_node->len field with the wrong sign, adding the header size instead of subtracting it. This accepts a declared length up to 2 * UBIFS_SIG_NODE_SZ larger than the node actually holds, leading to an out-of-bounds read past c->sbuf while processing the PKCS7 signature.
Risk Assessment
Mounting a crafted signed UBIFS image can cause an out-of-bounds read beyond the allocation, potentially disclosing kernel data or crashing the system.
Recommendation
Update the Linux kernel to a version containing the fix that corrects the signature length check.
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Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS