CVE-2021-45696: Sha2 Incorrect Hash Vulnerability

CRITICAL
Advisory Identifier: GHSA-fc7x-2cmc-8j2g
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CVSS 9.8
CWE-327
Published
Advisory Summary

CVE-2021-45696 is a CRITICAL (CVSS 9.8) incorrect hash vulnerability (CWE-327: Use of a Broken or Risky Cryptographic Algorithm) affecting Sha2 libraries in the crates.io ecosystem. The issue involves incorrect hash in sha2. Remediation is available by upgrading affected packages to version 0.9.8.

CVE-2021-45696 at a Glance

CVE Identifier CVE-2021-45696
GHSA Identifier GHSA-fc7x-2cmc-8j2g
Severity CRITICAL
CVSS v3.1 Base Score 9.8
CWE Classification CWE-327: Use of a Broken or Risky Cryptographic Algorithm
Affected Product Sha2
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-2021-45696

To remediate this vulnerability, upgrade all affected Sha2 dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

sha2 fixed: 0.9.8 
Upgrade sha2 to 0.9.8
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 sha2

How to Check if You Are Affected

To determine whether your application is affected by CVE-2021-45696, inspect your project dependencies for Sha2:

inspect dependencies for sha2

Analyze the terminal output to locate any version of Sha2 in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 0.9.8), 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-327: Use of a Broken or Risky Cryptographic Algorithm, where the product uses a broken or risky cryptographic algorithm or protocol. In Sha2, 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

The v0.9.7 release of the sha2 crate introduced a new AVX2-accelerated backend which was automatically enabled for all x86/x86_64 CPUs where AVX2 support was autodetected at runtime. This backend was buggy and would miscompute results for long messages (i.e. messages spanning multiple SHA blocks). The crate has since been yanked, but any users who upgraded to v0.9.7 should immediately upgrade to v0.9.8 and recompute any hashes which were previously computed by v0.9.7.

CVE-2021-45696 Affected Sha2 Versions

1 component(s)
Fixed Versions:
0.9.8
Product / Package Ecosystem Affected Versions Fixed Version
sha2
 crates.io
≥ 0.9.7
< 0.9.8
All 1 versions
0.9.7
0.9.8

References

NVD — CVE-2021-45696 NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-45696
Sha2 Source Repository REPOSITORY
https://github.com/RustCrypto/hashes/pull/314
Sha2 Source Repository REPOSITORY
https://github.com/RustCrypto/hashes
raw.githubusercontent.com/rustsec/advisory-db... WEB
https://raw.githubusercontent.com/rustsec/advisory-db/main/crates/sha2/RUSTSEC-2021-0100.md
rustsec.org/advisories/rustsec-... WEB
https://rustsec.org/advisories/RUSTSEC-2021-0100.html

Frequently Asked Questions

What is CVE-2021-45696?
CVE-2021-45696 is a security vulnerability in Sha2 involving Incorrect hash in sha2 under CWE-327: Use of a Broken or Risky Cryptographic Algorithm.
Which Sha2 versions are affected?
Affected versions include releases prior to 0.9.8 across affected packages: sha2.
What version fixes CVE-2021-45696?
Upgrading to 0.9.8 (or the latest patched release for your respective branch) resolves the vulnerability.
Is sha2 affected?
Yes, sha2 is affected in releases prior to 0.9.8. Upgrade your dependency to 0.9.8 or later.
What is the CVSS score of CVE-2021-45696?
CVE-2021-45696 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-2021-45696?
CVE-2021-45696 is classified under CWE-327: Use of a Broken or Risky Cryptographic Algorithm (The product uses a broken or risky cryptographic algorithm or protocol.).
How can I check crates.io dependencies for CVE-2021-45696?
Run the dependency tree command: 'inspect dependencies for sha2'. 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-fc7x-2cmc-8j2g",
  "modified" : "2023-06-13T20:41:36Z",
  "published" : "2022-01-06T22:10:26Z",
  "aliases" : [ "CVE-2021-45696" ],
  "summary" : "Incorrect hash in sha2",
  "details" : "The v0.9.7 release of the sha2 crate introduced a new AVX2-accelerated backend which was automatically enabled for all x86/x86_64 CPUs where AVX2 support was autodetected at runtime.\n\nThis backend was buggy and would miscompute results for long messages (i.e. messages spanning multiple SHA blocks).\n\nThe crate has since been yanked, but any users who upgraded to v0.9.7 should immediately upgrade to v0.9.8 and recompute any hashes which were previously computed by v0.9.7.",
  "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" : "sha2"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.9.7"
      }, {
        "fixed" : "0.9.8"
      } ]
    } ],
    "versions" : [ "0.9.7" ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-45696"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/RustCrypto/hashes/pull/314"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/RustCrypto/hashes"
  }, {
    "type" : "WEB",
    "url" : "https://raw.githubusercontent.com/rustsec/advisory-db/main/crates/sha2/RUSTSEC-2021-0100.md"
  }, {
    "type" : "WEB",
    "url" : "https://rustsec.org/advisories/RUSTSEC-2021-0100.html"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-327" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2022-01-06T14:26:28Z",
    "nvd_published_at" : "2021-12-27T00:15:00Z"
  }
}