CVE-2021-45696: An issue was discovered in the sha2 crate 0.9.7 before 0.9.8 for Rust

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CRITICAL 9.8REMOTEDOWNGRADE

CVE-2021-45696 is a critical-severity flaw (CVSS 9.8) affecting sha2. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

An issue was discovered in the sha2 crate 0.9.7 before 0.9.8 for Rust. Hashes of long messages may be incorrect when the AVX2-accelerated backend is used.

Why this priority

Critical severity
Remotely exploitable, no login, no user action

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.8% (top 42%)
CISA exploited list	No
Weakness	CWE-327
Published	2021-12-27
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: sha2 project

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

Am I affected?

Timeline

2021-12-27 00:15 UTCPublished CVE record published
2026-06-17 04:13 UTCUpdated Record last modified

sha2 project sha2 DOWNGRADE

Affected: 0.9.7

Fixed in: no fixed release known

Safe to downgrade to: a release before 0.9.7

1. Check installed version

apt-cache policy sha2 || rpm -q sha2 || sha2 --version

2. No fixed release: DOWNGRADE to a release before 0.9.7 (Debian / Ubuntu)

apt-cache madison sha2 sudo apt install sha2=<VERSION_BEFORE_0.9.7> sudo apt-mark hold sha2

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list sha2 sudo dnf downgrade sha2-<VERSION_BEFORE_0.9.7> sudo dnf versionlock add sha2

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

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-2021-45696?

sha2: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-45696 being exploited?

CVE-2021-45696 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-2021-45696 affect?

CVE-2021-45696 affects sha2. Severity is critical (CVSS 9.8). An issue was discovered in the sha2 crate 0.9.7 before 0.9.8 for Rust. Hashes of long messages may be incorrect when the AVX2-accelerated backend is used.

How urgent is CVE-2021-45696?

Priority 54/100. Critical severity; Remotely exploitable, no login, no user action

References

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