# CVE-2026-56409 — libexpat

> As of 2026-06-22, CVE-2026-56409 is a MEDIUM-severity vulnerability in libexpat, CVSS v3.1 6.5. No Threadlinqs-tracked threat campaign has been attributed to CVE-2026-56409 as of 2026-06-22; the identifier is re-checked against the Threadlinqs threat corpus on every daily ingest.

**Last updated:** 2026-06-22

## What is CVE-2026-56409?

xmlwf in libexpat before 2.8.2 has an integer overflow for the output filename when -d outputDir is used.

The record classifies CVE-2026-56409 under weakness class [CWE-190](https://intel.threadlinqs.com/cwe/CWE-190). Its CVSS v3 base vector states that the flaw requires local access to the host, needs no prior authentication, needs a user to take an action first, and has high impact on confidentiality, integrity. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 106 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 6.5 — MEDIUM (`CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:L`)
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 3.3/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-06-21, last modified 2026-06-22

## Is CVE-2026-56409 being exploited?

It currently carries a trending score of 30 in the Threadlinqs vulnerability feed.

## Affected products and versions

- [libexpat project](https://intel.threadlinqs.com/vendors/libexpat-project): libexpat

## How to fix CVE-2026-56409

No vendor patch reference has been recorded for CVE-2026-56409 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-2026-56409

No threat campaign in the Threadlinqs corpus currently references CVE-2026-56409, in its CVE list or as an indicator. The linkage is recomputed from the live corpus on every daily ingest, so this section fills in as soon as a tracked campaign cites the identifier.

## Sources

Enriched from CVE.org. Last verified by Threadlinqs on 2026-06-22.

**Other references**

- [github.com](https://github.com/libexpat/libexpat/pull/1259)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-56409
Full detection coverage and IOCs for threats exploiting CVE-2026-56409 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp