CVE-2021-21828Network attack vector

Code execution via unchecked label-pointer increment

Published Aug 20, 2021 · Updated Aug 3, 2024

Heap-based buffer overflow in AT&T Labs Xmill 0.7 allows attackers to execute code by decompressing a crafted XMI file. DecodeTreeBlock passes each default-case label to CurPath::AddLabel, which increments an unchecked global pointer and writes attacker-controlled two-byte label identifiers beyond its buffer. Exploitation requires a user or application to process the crafted file with Xdemill; the resulting overwrite can redirect execution on the host.

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 attackers to execute code by decompressing a crafted XMI file. DecodeTreeBlock passes each default-case label to CurPath::AddLabel, which increments an unchecked global pointer and writes attacker-controlled two-byte label identifiers beyond its buffer. Exploitation requires a user or application to process the crafted file with Xdemill; the resulting overwrite can redirect execution on the host.

The record

CVE
CVE-2021-21828
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

8.1Cisco TalosCVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
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

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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