CVE-2021-26956: An issue was discovered in the xcb crate through 2021-02-04 for Rust

Q: How do I fix CVE-2021-26956?

xcb: upgrade to newer than 2021-02-04. Exact commands for each OS are on this page.

Q: Is CVE-2021-26956 being exploited?

CVE-2021-26956 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-26956 affect?

CVE-2021-26956 affects xcb. Severity is critical (CVSS 9.8). An issue was discovered in the xcb crate through 2021-02-04 for Rust. It has a soundness violation because bytes from an X server can be interpreted as any data type returned by xcb::xproto::GetPropertyReply::value.

Q: How urgent is CVE-2021-26956?

Priority 64/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

This week

CRITICAL 9.8REMOTEUPGRADE

CVE-2021-26956 is a critical-severity flaw (CVSS 9.8) affecting xcb. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

An issue was discovered in the xcb crate through 2021-02-04 for Rust. It has a soundness violation because bytes from an X server can be interpreted as any data type returned by xcb::xproto::GetPropertyReply::value.

Why this priority

Critical severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.7% (top 22%)
CISA exploited list	No
Published	2021-02-09
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: xcb project

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

Am I affected?

Timeline

2021-02-09 23:15 UTCPublished CVE record published
2026-06-17 03:44 UTCUpdated Record last modified

xcb project xcb UPGRADE

Affected: <= 2021-02-04

Fixed in: newer than 2021-02-04

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to newer than 2021-02-04 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade xcb

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade xcb

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

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-2021-26956?

xcb: upgrade to newer than 2021-02-04. Exact commands for each OS are on this page.

Is CVE-2021-26956 being exploited?

CVE-2021-26956 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-2021-26956 affect?

CVE-2021-26956 affects xcb. Severity is critical (CVSS 9.8). An issue was discovered in the xcb crate through 2021-02-04 for Rust. It has a soundness violation because bytes from an X server can be interpreted as any data type returned by xcb::xproto::GetPropertyReply::value.

How urgent is CVE-2021-26956?

Priority 64/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

CVE-2021-26958 HIGH 8.8 UPGRADE An issue was discovered in the xcb crate through 2021-02-04 for Rust
CVE-2021-26957 CRITICAL 9.8 UPGRADE An issue was discovered in the xcb crate through 2021-02-04 for Rust
CVE-2021-26955 CRITICAL 9.8 UPGRADE An issue was discovered in the xcb crate through 2021-02-04 for Rust
CVE-2020-36205 MEDIUM 5.5 UPGRADE An issue was discovered in the xcb crate through 2020-12-10 for Rust

References

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