# CVE-2026-45991 — Linux

> As of 2026-08-05, CVE-2026-45991 is a HIGH-severity vulnerability in Linux, CVSS v3.1 7.8, EPSS 0.1% (5.6th percentile). Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2026-45991, most recently “F5 F5OS 2.0.0 Affected by Linux Kernel UDF Partition Descriptor Heap Out-of-Bounds Write (CVE-2026-45991)”.

**Last updated:** 2026-08-05

## What is CVE-2026-45991?

In the Linux kernel, the following vulnerability has been resolved: udf: fix partition descriptor append bookkeeping Mounting a crafted UDF image with repeated partition descriptors can trigger a heap out-of-bounds write in part_descs_loc[]. handle_partition_descriptor() deduplicates entries by partition number, but appended slots never record partnum. As a result duplicate Partition Descriptors are appended repeatedly and num_part_descs keeps growing. Once the table is full, the growth path still sizes the allocation from partnum even though inserts are indexed by num_part_descs. If partnum is already aligned to PART_DESC_ALLOC_STEP, ALIGN(partnum, step) can keep the old capacity and the next append writes past the end of the table. Store partnum in the appended slot and size growth from the next append count so deduplication and capacity tracking follow the same model.

Its CVSS v3 base vector states that the flaw requires local access to the host, needs low-privilege credentials, needs no user interaction, and has high impact on confidentiality, integrity, availability. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 136 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 7.8 — HIGH (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **EPSS (FIRST):** 0.1% probability of exploitation in the next 30 days, higher than 5.6% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 4.1/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-05-27, last modified 2026-08-05

## Is CVE-2026-45991 being exploited?

It currently carries a trending score of 6 in the Threadlinqs vulnerability feed.

## Affected products and versions

- [Linux](https://intel.threadlinqs.com/vendors/linux): Linux

## How to fix CVE-2026-45991

No vendor patch reference has been recorded for CVE-2026-45991 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-45991

1 tracked threat in the Threadlinqs corpus references CVE-2026-45991, either in the campaign’s CVE list or as an indicator on the campaign record.

- [F5 F5OS 2.0.0 Affected by Linux Kernel UDF Partition Descriptor Heap Out-of-Bounds Write (CVE-2026-45991)](https://intel.threadlinqs.com/threat/TL-2026-3274) — HIGH · 2026-10-10

## Sources

Enriched from CVE.org, FIRST EPSS, GitHub Security Advisories. Last verified by Threadlinqs on 2026-10-10.

**Other references**

- [git.kernel.org](https://git.kernel.org/stable/c/ad3c0c4400686f6f37b382aaa48fac2b9aefccbe)
- [git.kernel.org (68013a9bd4c01acd42073715f00e1a1992f089ee)](https://git.kernel.org/stable/c/68013a9bd4c01acd42073715f00e1a1992f089ee)
- [git.kernel.org (e8474cfbac9ada2cdaa4eaedec22aadfa0f58559)](https://git.kernel.org/stable/c/e8474cfbac9ada2cdaa4eaedec22aadfa0f58559)
- [git.kernel.org (058b451b1039f056d1362c4fec2229e522366ab0)](https://git.kernel.org/stable/c/058b451b1039f056d1362c4fec2229e522366ab0)
- [git.kernel.org (b5597bb83fc37b5b5da74a4453fa920b932cf39a)](https://git.kernel.org/stable/c/b5597bb83fc37b5b5da74a4453fa920b932cf39a)

_Showing 5 of 7 recorded references._

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-45991
Full detection coverage and IOCs for threats exploiting CVE-2026-45991 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp