CVE-2021-21826

Name: CVE-2021-21826
Creator: NVD / NIST
Published: 2021-08-20T22:15:07.067+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.8/10EPSS 1.14%

Last modified Jun 17, 2026

CVE-2021-21826 is a critical-severity vulnerability rated 9.8/10 on the CVSS scale. A heap-based buffer overflow vulnerability exists in the XML Decompression DecodeTreeBlock functionality of AT&T Labs Xmill 0.7. Within `DecodeTreeBlock` which is called during the decompression of an XMI file, a UINT32 is loaded from the file and used as trusted input as the length of a buffer. EPSS estimates a 1.14% chance of exploitation in the next 30 days.

Description

A heap-based buffer overflow vulnerability exists in the XML Decompression DecodeTreeBlock functionality of AT&T Labs Xmill 0.7. Within `DecodeTreeBlock` which is called during the decompression of an XMI file, a UINT32 is loaded from the file and used as trusted input as the length of a buffer. An attacker can provide a malicious file to trigger this vulnerability.

Metrics

CVSS 3.1

9.8/10

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

EPSS Probability

1.14%

62.5th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Att	Xmill	0.7

References

https://talosintelligence.com/vulnerability_reports/TALOS-2021-1291Exploit, Third Party Advisory
https://talosintelligence.com/vulnerability_reports/TALOS-2021-1291Exploit, Third Party Advisory

Timeline

Published: Aug 20, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-21826?

How severe is CVE-2021-21826?

CVE-2021-21826 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 1.14% probability of exploitation in the next 30 days.

How do I fix CVE-2021-21826?

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.

Are you affected by CVE-2021-21826?

Run a free Strix scan to check your systems for this vulnerability.

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Source: NVD / NIST