CVE-2021-21813: Within the function HandleFileArg the argument filepattern is under control of the user who passes it in from

Routine

HIGH 7.8DOWNGRADE

CVE-2021-21813 is a high-severity flaw (CVSS 7.8) affecting xmill. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Within the function HandleFileArg the argument filepattern is under control of the user who passes it in from the command line. filepattern is passed directly to memcpy copying the path provided by the user into a staticly sized buffer without any length checks resulting in a stack-buffer overflow.

Why this priority

High severity
Public exploit reference

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	7.8 (High)
Attack vector	Local
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.3% (top 73%)
CISA exploited list	No
Weakness	CWE-787
Published	2021-08-13
Last modified	2026-06-17

Publisher (CNA): Talos · Vendor: att

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-08-13 23:15 UTCPublished CVE record published
2026-06-17 03:36 UTCUpdated Record last modified

att xmill DOWNGRADE

Affected: 0.7

Fixed in: no fixed release known

Safe to downgrade to: a release before 0.7

1. Check installed version

apt-cache policy xmill || rpm -q xmill || xmill --version

2. No fixed release: DOWNGRADE to a release before 0.7 (Debian / Ubuntu)

apt-cache madison xmill sudo apt install xmill=<VERSION_BEFORE_0.7> sudo apt-mark hold xmill

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list xmill sudo dnf downgrade xmill-<VERSION_BEFORE_0.7> sudo dnf versionlock add xmill

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-21813?

xmill: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-21813 being exploited?

CVE-2021-21813 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-21813 affect?

CVE-2021-21813 affects xmill. Severity is high (CVSS 7.8). Within the function HandleFileArg the argument filepattern is under control of the user who passes it in from the command line. filepattern is passed directly to memcpy copying the path provided by the user into a staticly sized buffer with

How urgent is CVE-2021-21813?

Priority 39/100. High severity; Public exploit reference

Related CVEs

CVE-2022-26507 CRITICAL 9.8 DOWNGRADE UPGRADE A heap-based buffer overflow exists in XML Decompression DecodeTreeBlock in AT&T Labs Xmill 0.7
CVE-2021-21830 CRITICAL 9.8 DOWNGRADE A heap-based buffer overflow vulnerability exists in the XML Decompression LabelDict::Load functionality of AT
CVE-2021-21829 CRITICAL 9.8 DOWNGRADE A heap-based buffer overflow vulnerability exists in the XML Decompression EnumerationUncompressor::Uncompress
CVE-2021-21828 CRITICAL 9.8 DOWNGRADE A heap-based buffer overflow vulnerability exists in the XML Decompression DecodeTreeBlock functionality of AT
CVE-2021-21827 CRITICAL 9.8 DOWNGRADE A heap-based buffer overflow vulnerability exists in the XML Decompression DecodeTreeBlock functionality of AT

References

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