CVE-2026-89720 ubifs: fix out-of-bounds read in signature length check
A crafted UBIFS image triggers an out-of-bounds read in the kernel signature verification, potentially leaking memory contents.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-89720?
CVE-2026-89720 is a high-severity vulnerability in Linux, published on 11 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
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.
Which versions are affected by CVE-2026-89720?
How do I fix CVE-2026-89720?
Apply the vendor's patch.
Is CVE-2026-89720 being exploited?
There is no known exploitation of CVE-2026-89720 in the wild and no public exploit code.
Sources
Also known as AZL-100085, BELL-CVE-2026-89720, DEBIAN-CVE-2026-89720, GHSA-8388-259p-82vg, UBUNTU-CVE-2026-89720.