CVE-2021-25948: Prototype pollution vulnerability in 'expand-hash' versions 0.1.0 through 1.0.1 allows an attacker to cause a

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CRITICAL 9.8REMOTEUPGRADE

CVE-2021-25948 is a critical-severity flaw (CVSS 9.8) affecting expand-hash. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Prototype pollution vulnerability in 'expand-hash' versions 0.1.0 through 1.0.1 allows an attacker to cause a denial of service and may lead to remote code execution.

Why this priority

Critical severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	3.3% (top 11%)
CISA exploited list	No
Weakness	CWE-1321
Published	2021-06-10
Last modified	2026-06-17

Publisher (CNA): Mend · Vendor: expand-hash project

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

Am I affected?

Timeline

2021-06-10 12:15 UTCPublished CVE record published
2026-06-17 03:42 UTCUpdated Record last modified

expand-hash project expand-hash UPGRADE

Affected: >= 0.1.0 and <= 1.0.1

Fixed in: newer than 1.0.1

Safe to downgrade to: a release before 0.1.0

1. Check installed version

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

2. UPGRADE to newer than 1.0.1 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade expand-hash

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade expand-hash

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 0.1.0 (Debian / Ubuntu)

apt-cache madison expand-hash sudo apt install expand-hash=<VERSION_BEFORE_0.1.0> sudo apt-mark hold expand-hash

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list expand-hash sudo dnf downgrade expand-hash-<VERSION_BEFORE_0.1.0> sudo dnf versionlock add expand-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-2021-25948?

expand-hash: upgrade to newer than 1.0.1. Exact commands for each OS are on this page.

Is CVE-2021-25948 being exploited?

CVE-2021-25948 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-2021-25948 affect?

CVE-2021-25948 affects expand-hash. Severity is critical (CVSS 9.8). Prototype pollution vulnerability in 'expand-hash' versions 0.1.0 through 1.0.1 allows an attacker to cause a denial of service and may lead to remote code execution.

How urgent is CVE-2021-25948?

Priority 66/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

References

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