CVE-2026-89720 Affecting linux-6.12 package, versions <6.12.111-1~deb12u1


Severity

Recommended
low

Based on default assessment until relevant scores are available.

Threat Intelligence

EPSS
0.19% (8th percentile)

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  • Snyk IDSNYK-DEBIAN12-LINUX612-20507148
  • published5 Oct 2026
  • disclosed11 Sept 2026

Introduced: 11 Sep 2026

NewCVE-2026-89720  (opens in a new tab)

How to fix?

Upgrade Debian:12 linux-6.12 to version 6.12.111-1~deb12u1 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream linux-6.12 package and not the linux-6.12 package as distributed by Debian. See How to fix? for Debian:12 relevant fixed versions and status.

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-&gt;len) &gt; snod-&gt;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-&gt;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.

CVSS Base Scores

version 3.1