CVE-2021-26957: Xcb Out Of Bounds Read Vulnerability

CRITICAL
Advisory Identifier: GHSA-2xpg-3hx4-fm9r
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CVSS 9.8
CWE-125
Published
Advisory Summary

CVE-2021-26957 is a CRITICAL (CVSS 9.8) out of bounds read vulnerability (CWE-125: Out-of-bounds Read) affecting Xcb libraries in the crates.io ecosystem. The issue involves out of bounds read in xcb. Remediation is available by upgrading affected packages to version 1.0.0.

CVE-2021-26957 at a Glance

CVE Identifier CVE-2021-26957
GHSA Identifier GHSA-2xpg-3hx4-fm9r
Severity CRITICAL
CVSS v3.1 Base Score 9.8
CWE Classification CWE-125: Out-of-bounds Read
Affected Product Xcb
Package Ecosystem crates.io
Published Date
Last Updated

Security Impact

CVSS: 9.8

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity High (I:H)
Availability High (A:H)

How to Fix CVE-2021-26957

To remediate this vulnerability, upgrade all affected Xcb dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

xcb fixed: 1.0.0 
Upgrade xcb to 1.0.0
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for xcb

How to Check if You Are Affected

To determine whether your application is affected by CVE-2021-26957, inspect your project dependencies for Xcb:

inspect dependencies for xcb

Analyze the terminal output to locate any version of Xcb in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.0.0), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-125: Out-of-bounds Read, where the product reads data past the end, or before the beginning, of the intended buffer. In Xcb, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

An issue was discovered in the xcb crate through 2021-02-04 for Rust. It has a soundness violation because there is an out-of-bounds read in xcb::xproto::change_property(), as demonstrated by a format=32 T=u8 situation where out-of-bounds bytes are sent to an X server.

CVE-2021-26957 Affected Xcb Versions

1 component(s)
Fixed Versions:
1.0.0
Product / Package Ecosystem Affected Versions Fixed Version
xcb
 crates.io
< 1.0.0
1.0.0

References

NVD — CVE-2021-26957 NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-26957
Xcb Source Repository REPOSITORY
https://github.com/RustSec/advisory-db/issues/653
Xcb Source Repository REPOSITORY
https://github.com/rtbo/rust-xcb
rustsec.org/advisories/rustsec-... WEB
https://rustsec.org/advisories/RUSTSEC-2021-0019.html

Frequently Asked Questions

What is CVE-2021-26957?
CVE-2021-26957 is a security vulnerability in Xcb involving Out of bounds read in xcb under CWE-125: Out-of-bounds Read.
Which Xcb versions are affected?
Affected versions include releases prior to 1.0.0 across affected packages: xcb.
What version fixes CVE-2021-26957?
Upgrading to 1.0.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is xcb affected?
Yes, xcb is affected in releases prior to 1.0.0. Upgrade your dependency to 1.0.0 or later.
What is the CVSS score of CVE-2021-26957?
CVE-2021-26957 has a CVSS v3.1 base score of 9.8 (CRITICAL) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
What CWE is associated with CVE-2021-26957?
CVE-2021-26957 is classified under CWE-125: Out-of-bounds Read (The product reads data past the end, or before the beginning, of the intended buffer.).
How can I check crates.io dependencies for CVE-2021-26957?
Run the dependency tree command: 'inspect dependencies for xcb'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-2xpg-3hx4-fm9r",
  "modified" : "2021-08-19T17:44:08Z",
  "published" : "2021-08-25T20:53:20Z",
  "aliases" : [ "CVE-2021-26957" ],
  "summary" : "Out of bounds read in xcb",
  "details" : "An issue was discovered in the xcb crate through 2021-02-04 for Rust. It has a soundness violation because there is an out-of-bounds read in xcb::xproto::change_property(), as demonstrated by a format=32 T=u8 situation where out-of-bounds bytes are sent to an X server.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "xcb"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.0.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-26957"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/RustSec/advisory-db/issues/653"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/rtbo/rust-xcb"
  }, {
    "type" : "WEB",
    "url" : "https://rustsec.org/advisories/RUSTSEC-2021-0019.html"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-125" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2021-08-19T17:44:08Z",
    "nvd_published_at" : null
  }
}