CVE-2021-26955Network attack vector

Memory unsafety via unvalidated X atom names

Published Feb 9, 2021 · Updated Aug 3, 2024

Soundness violation in the Rust xcb crate before 1.0.0 allows remote attackers controlling an X server to induce memory unsafety. GetAtomNameReply::name() passes raw atom-name bytes to std::str::from_utf8_unchecked() without validating UTF-8 before returning an &str. Exploitation requires a client to request an attacker-controlled atom name, exposing consuming code to undefined behavior.

CVSS severity9.8
Critical
EPSS probability1.73%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Soundness violation in the Rust xcb crate before 1.0.0 allows remote attackers controlling an X server to induce memory unsafety. GetAtomNameReply::name() passes raw atom-name bytes to std::str::from_utf8_unchecked() without validating UTF-8 before returning an &str. Exploitation requires a client to request an attacker-controlled atom name, exposing consuming code to undefined behavior.

The record

CVE
CVE-2021-26955
Published
Feb 9, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-252
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 9, 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

9.8GitHub Advisory DatabaseCVSS: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.

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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-252Unchecked Return Value

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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