CVE-2021-37606: Meow hash 0.5/calico does not sufficiently thwart key recovery by an attacker who can query whether there's a

Routine

MEDIUM 5.3REMOTEDOWNGRADE

CVE-2021-37606 is a medium-severity flaw (CVSS 5.3) affecting meow hash. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Meow hash 0.5/calico does not sufficiently thwart key recovery by an attacker who can query whether there's a collision in the bottom bits of the hashes of two messages, as demonstrated by an attack against a long-running web service that allows the attacker to infer collisions by measuring timing differences.

Why this priority

Remotely exploitable, no login, no user action

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

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.7% (top 45%)
CISA exploited list	No
Weakness	CWE-203, CWE-326
Published	2021-07-30
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: meow hash project

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

Am I affected?

Timeline

2021-07-30 14:15 UTCPublished CVE record published
2026-06-17 04:00 UTCUpdated Record last modified

meow hash project meow hash DOWNGRADE

Affected: 0.5

Fixed in: no fixed release known

Safe to downgrade to: a release before 0.5

1. Check installed version

apt-cache policy meow-hash || rpm -q meow-hash || meow-hash --version

2. No fixed release: DOWNGRADE to a release before 0.5 (Debian / Ubuntu)

apt-cache madison meow-hash sudo apt install meow-hash=<VERSION_BEFORE_0.5> sudo apt-mark hold meow-hash

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

dnf --showduplicates list meow-hash sudo dnf downgrade meow-hash-<VERSION_BEFORE_0.5> sudo dnf versionlock add meow-hash

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-2021-37606?

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

Is CVE-2021-37606 being exploited?

CVE-2021-37606 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-2021-37606 affect?

CVE-2021-37606 affects meow hash. Severity is medium (CVSS 5.3). Meow hash 0.5/calico does not sufficiently thwart key recovery by an attacker who can query whether there's a collision in the bottom bits of the hashes of two messages, as demonstrated by an attack against a long-running web service that a

How urgent is CVE-2021-37606?

Priority 37/100. Remotely exploitable, no login, no user action

References

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