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CVE-2026-89720

HIGHCVSS 7.7/10EPSS 0.18%

Last modified

CVE-2026-89720 is a high-severity vulnerability rated 7.7/10 on the CVSS scale. 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. EPSS estimates a 0.18% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1
7.7/10

CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H

EPSS Probability
0.18%

8.0th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

VendorProductVersions
LinuxLinux>= 817aa094842dfc3a6b98c9582d4a647827f66201, < ab7405bd86331cc2dbc8201699d4adc33bea75e7; >= 817aa094842dfc3a6b98c9582d4a647827f66201, < 11abc34698cb3172badf8aa12e623f1bac98bbd8; >= 817aa094842dfc3a6b98c9582d4a647827f66201, < 8cc3da72cf57acb4b77442ea8cec48425dff7c06; >= 817aa094842dfc3a6b98c9582d4a647827f66201, < 37a9d25a563f5f9103282954ce573c4a61321e7c; >= 817aa094842dfc3a6b98c9582d4a647827f66201, < f76b79d6e42af20682495bccd22f72c7164b0018; >= 817aa094842dfc3a6b98c9582d4a647827f66201, < a1dc246f98bb94233effa4fa3ec7bf84700bb7d1; >= 817aa094842dfc3a6b98c9582d4a647827f66201, < 83e1aa9f5f906c9b1f4949d0521f0f950a159d96; >= 817aa094842dfc3a6b98c9582d4a647827f66201, < 95d27c1708bb6e8823c8e7c623f9abc2a91bf4bf
LinuxLinux5.3

References

Timeline

Published
Last Modified
Status
Received

Frequently Asked Questions

What is CVE-2026-89720?
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.
How severe is CVE-2026-89720?
CVE-2026-89720 has a CVSS score of 7.7/10 (HIGH severity). The EPSS model estimates a 0.18% probability of exploitation in the next 30 days.
How do I fix CVE-2026-89720?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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Source: NVD / NIST