---
title: "CVE-2026-93990: Expat - XML Injection"
description: "Expat through 2.8.4 contains an XML injection vulnerability caused by failure to validate low surrogates following high surrogates in UTF-16 input, letting attackers craft malformed UTF-16 sequences to hide markup characters, exploit requires crafted UTF-16 encoded XML."
url: https://panop.io/threat-heartbeat/CVE-2026-93990/
---

# CVE-2026-93990 Expat - XML Injection

Expat through 2.8.4 contains an XML injection vulnerability caused by failure to validate low surrogates following high surrogates in UTF-16 input, letting attackers craft malformed UTF-16 sequences to hide markup characters, exploit requires crafted UTF-16 encoded XML.

CVSS base score 7.5 /10

High

CISA KEV

Not listed

Public exploit

None known

Authentication

Not required

EPSS

0.40% chance of exploitation in 30 days

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-93990)

## Details

Type

XML Injection

Impact

Data Tampering

CVSS vector

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

Published

19 September 2026

Updated

15 October 2026

Weakness

[CWE-176](https://cwe.mitre.org/data/definitions/176.html)

## Vendor fix

Update to the latest version beyond 2.8.4.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

## References

- [https://nvd.nist.gov/vuln/detail/CVE-2026-93990](https://nvd.nist.gov/vuln/detail/CVE-2026-93990)
- [https://github.com/libexpat/libexpat/commit/ff6e1d7e750bbe245178f51a47a965dc8342861a](https://github.com/libexpat/libexpat/commit/ff6e1d7e750bbe245178f51a47a965dc8342861a)
- [https://github.com/libexpat/libexpat/pull/1282](https://github.com/libexpat/libexpat/pull/1282)
- [https://www.vulncheck.com/advisories/expat-through-2.8.4-malformed-utf-16-acceptance-via-unchecked-surrogate](https://www.vulncheck.com/advisories/expat-through-2.8.4-malformed-utf-16-acceptance-via-unchecked-surrogate)
- [https://blog.hartwork.org/posts/expat-2-8-5-released/](https://blog.hartwork.org/posts/expat-2-8-5-released/)
- [https://github.com/libexpat/libexpat/releases/tag/R\_2\_8\_5](https://github.com/libexpat/libexpat/releases/tag/R_2_8_5)
- [https://github.com/libexpat/libexpat](https://github.com/libexpat/libexpat)

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## What this record can't tell you

- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
- What it would cost the business, ranked into what to fix first

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