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Vulnerability record · CVE-2021-21826 · published 20 August 2021

CVE-2021-21826: Att xmill classic buffer overflow vulnerability

Att · Xmill

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.

9.8 CVSS 3.1 Critical EPSS 1.1% · top 34.8% CWE-120 · Classic buffer overflowCWE-787 · Out-of-bounds write
9.8CVSS 3.1 base score, v2 7.5
1.1%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
2References, 2 tagged exploit
17 Jun 2026Last modified by NVD

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.

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

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://talosintelligence.com/vulnerability_reports/TALOS-2021-1291 ExploitThird Party Advisory
https://talosintelligence.com/vulnerability_reports/TALOS-2021-1291 ExploitThird Party Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

9.8CVE-2022-26507Att xmill out-of-bounds write vulnerabilityA heap-based buffer overflow exists in XML Decompression DecodeTreeBlock in AT&T Labs Xmill 0.7. A crafted input file can lead to remote code executi…EPSS 2.4%9.8CVE-2021-21811Att xmill vulnerabilityA memory corruption vulnerability exists in the XML-parsing CreateLabelOrAttrib functionality of AT&T Labs’ Xmill 0.7. A specially crafted XML file c…EPSS 1.1%9.8CVE-2021-21827Att xmill classic buffer overflow vulnerabilityA heap-based buffer overflow vulnerability exists in the XML Decompression DecodeTreeBlock functionality of AT&T Labs Xmill 0.7. Within `DecodeTreeBl…EPSS 1.1%9.8CVE-2021-21828Att xmill classic buffer overflow vulnerabilityA heap-based buffer overflow vulnerability exists in the XML Decompression DecodeTreeBlock functionality of AT&T Labs Xmill 0.7. In the default case …EPSS 1.1%9.8CVE-2021-21825Att xmill heap-based buffer overflow vulnerabilityA heap-based buffer overflow vulnerability exists in the XML Decompression PlainTextUncompressor::UncompressItem functionality of AT&T Labs’ Xmill 0.…EPSS 2.3%9.8CVE-2021-21810Att xmill heap-based buffer overflow vulnerabilityA memory corruption vulnerability exists in the XML-parsing ParseAttribs functionality of AT&T Labs’ Xmill 0.7. A specially crafted XML file can lead…EPSS 1.1%9.8CVE-2021-21829Att xmill heap-based buffer overflow vulnerabilityA heap-based buffer overflow vulnerability exists in the XML Decompression EnumerationUncompressor::UncompressItem functionality of AT&T Labs’ Xmill …EPSS 2.5%9.8CVE-2021-21830Att xmill heap-based buffer overflow vulnerabilityA heap-based buffer overflow vulnerability exists in the XML Decompression LabelDict::Load functionality of AT&T Labs’ Xmill 0.7. A specially crafted…EPSS 2.3%

Source: NIST National Vulnerability Database (record CVE-2021-21826), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.