CVE-2021-21830Network attack vector

Code execution via misaccounted alignment padding

Published Aug 13, 2021 · Updated Aug 3, 2024

Heap-based buffer overflow in AT&T Labs XMill 0.7 allows attackers to execute arbitrary code while decompressing a crafted XMI file. In LabelDict::Load, MemStreamer::WordAlign advances the heap cursor after GetByteBlock reserves space without accounting correctly for the alignment, allowing repeated label copies to write past the allocation. Exploitation requires the decompressor to process an attacker-supplied XMI file; a successful overwrite executes code in the xdemill process context.

CVSS severity9.8
Critical
EPSS probability2.27%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Heap-based buffer overflow in AT&T Labs XMill 0.7 allows attackers to execute arbitrary code while decompressing a crafted XMI file. In LabelDict::Load, MemStreamer::WordAlign advances the heap cursor after GetByteBlock reserves space without accounting correctly for the alignment, allowing repeated label copies to write past the allocation. Exploitation requires the decompressor to process an attacker-supplied XMI file; a successful overwrite executes code in the xdemill process context.

The record

CVE
CVE-2021-21830
Published
Aug 13, 2021
Updated
Aug 3, 2024
Vendor
AT&T Labs
Product
XMill
Classifications
CWE-122, CWE-787, T1204.002, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 13, 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

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=AT&T Labs Xmill 0.7

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

AT&T Labs · XMillversion=AT&T Labs Xmill 0.7

Published CVSS scores

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

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-122Heap-based Buffer Overflow
CWE-787Out-of-bounds Write
T1204.002User Execution: Malicious File
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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo