CVE-2021-27378: Rand core Incorrect Check On Buffer Length Vulnerability

CRITICAL
Advisory Identifier: GHSA-w7j2-35mf-95p7
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CVSS 9.8
CWE-330
Published
Advisory Summary

CVE-2021-27378 is a CRITICAL (CVSS 9.8) incorrect check on buffer length vulnerability (CWE-330: Use of Insufficiently Random Values) affecting Rand core libraries in the crates.io ecosystem. The issue involves incorrect check on buffer length in rand_core. Remediation is available by upgrading affected packages to version 0.6.2.

CVE-2021-27378 at a Glance

CVE Identifier CVE-2021-27378
GHSA Identifier GHSA-w7j2-35mf-95p7
Severity CRITICAL
CVSS v3.1 Base Score 9.8
CWE Classification CWE-330: Use of Insufficiently Random Values
Affected Product Rand core
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-2021-27378

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

rand_core fixed: 0.6.2 
Upgrade rand_core to 0.6.2
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 rand_core

How to Check if You Are Affected

To determine whether your application is affected by CVE-2021-27378, inspect your project dependencies for Rand core:

inspect dependencies for rand_core

Analyze the terminal output to locate any version of Rand core in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 0.6.2), 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-330: Use of Insufficiently Random Values, where the product uses insufficiently random numbers or values in a security context that depends on unpredictable numbers. In Rand core, 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 rand_core crate before 0.6.2 for Rust. Because `read_u32_into` and `read_u64_into` mishandle certain buffer-length checks, a random number generator may be seeded with too little data. The vulnerability was introduced in v0.6.0. The advisory doesn't apply to earlier minor version numbers. Because read_u32_into and read_u64_into mishandle certain buffer-length checks, a random number generator may be seeded with too little data.

CVE-2021-27378 Affected Rand core Versions

1 component(s)
Fixed Versions:
0.6.2
Product / Package Ecosystem Affected Versions Fixed Version
rand_core
 crates.io
≥ 0.6.0
< 0.6.2
0.6.2

References

NVD — CVE-2021-27378 NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-27378
Rand core Source Repository REPOSITORY
https://github.com/rust-random/rand/pull/1096
Rand core Source Repository REPOSITORY
https://github.com/rust-random/rand
Rand core Source Repository REPOSITORY
https://github.com/rust-random/rand/compare/0.6.0...rand_core-0.6.2#diff-f41b3dfa5ce28f3bee390d327c50621e141cf3569921f8e9ca15ccfcf25263a9R19
Rand core Source Repository REPOSITORY
https://github.com/rust-random/rand/compare/0.6.0...rand_core-0.6.2#diff-f41b3dfa5ce28f3bee390d327c50621e141cf3569921f8e9ca15ccfcf25263a9R28
rustsec.org/advisories/rustsec-... WEB
https://rustsec.org/advisories/RUSTSEC-2021-0023.html

Frequently Asked Questions

What is CVE-2021-27378?
CVE-2021-27378 is a security vulnerability in Rand core involving Incorrect check on buffer length in rand_core under CWE-330: Use of Insufficiently Random Values.
Which Rand core versions are affected?
Affected versions include releases prior to 0.6.2 across affected packages: rand_core.
What version fixes CVE-2021-27378?
Upgrading to 0.6.2 (or the latest patched release for your respective branch) resolves the vulnerability.
Is rand_core affected?
Yes, rand_core is affected in releases prior to 0.6.2. Upgrade your dependency to 0.6.2 or later.
What is the CVSS score of CVE-2021-27378?
CVE-2021-27378 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-2021-27378?
CVE-2021-27378 is classified under CWE-330: Use of Insufficiently Random Values (The product uses insufficiently random numbers or values in a security context that depends on unpredictable numbers.).
How can I check crates.io dependencies for CVE-2021-27378?
Run the dependency tree command: 'inspect dependencies for rand_core'. 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-w7j2-35mf-95p7",
  "modified" : "2022-07-13T20:03:17Z",
  "published" : "2021-08-25T20:52:16Z",
  "aliases" : [ "CVE-2021-27378" ],
  "summary" : "Incorrect check on buffer length in rand_core",
  "details" : "An issue was discovered in the rand_core crate before 0.6.2 for Rust. Because `read_u32_into` and `read_u64_into` mishandle certain buffer-length checks, a random number generator may be seeded with too little data. The vulnerability was introduced in v0.6.0. The advisory doesn't apply to earlier minor version numbers.\n\nBecause read_u32_into and read_u64_into mishandle certain buffer-length checks, a random number generator may be seeded with too little data.",
  "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" : "rand_core"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.6.0"
      }, {
        "fixed" : "0.6.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-27378"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rust-random/rand/pull/1096"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/rust-random/rand"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rust-random/rand/compare/0.6.0...rand_core-0.6.2#diff-f41b3dfa5ce28f3bee390d327c50621e141cf3569921f8e9ca15ccfcf25263a9R19"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rust-random/rand/compare/0.6.0...rand_core-0.6.2#diff-f41b3dfa5ce28f3bee390d327c50621e141cf3569921f8e9ca15ccfcf25263a9R28"
  }, {
    "type" : "WEB",
    "url" : "https://rustsec.org/advisories/RUSTSEC-2021-0023.html"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-330" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2021-08-19T17:35:01Z",
    "nvd_published_at" : "2021-02-18T04:15:00Z"
  }
}