CVE-2021-21826Network attack vector

Remote code execution via untrusted decompression length

Published Aug 20, 2021 · Updated Aug 3, 2024

Heap-based buffer overflow in AT&T Labs Xmill 0.7 allows remote attackers to execute arbitrary code through a crafted XMI file. DecodeTreeBlock reads a UINT32 from the file and trusts it as a buffer length without validating it against the available decompressed data, enabling a heap overwrite. The attacker must supply an XMI file for decompression; successful corruption grants code execution in the context of the Xmill-consuming process.

CVSS severity8.1
High
EPSS probability1.14%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap-based buffer overflow in AT&T Labs Xmill 0.7 allows remote attackers to execute arbitrary code through a crafted XMI file. DecodeTreeBlock reads a UINT32 from the file and trusts it as a buffer length without validating it against the available decompressed data, enabling a heap overwrite. The attacker must supply an XMI file for decompression; successful corruption grants code execution in the context of the Xmill-consuming process.

The record

CVE
CVE-2021-21826
Published
Aug 20, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-120, CWE-787, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 20, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P
9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
8.1Cisco TalosCVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
CWE-787Out-of-bounds Write
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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