CVE-2021-25953: Prototype pollution vulnerability in 'putil-merge' versions1.0.0 through 3.6.6 allows attacker to cause a deni

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CRITICAL 9.8REMOTEUPGRADE

CVE-2021-25953 is a critical-severity flaw (CVSS 9.8) affecting putil-merge. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Prototype pollution vulnerability in 'putil-merge' versions1.0.0 through 3.6.6 allows 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	3.0% (top 13%)
CISA exploited list	No
Weakness	CWE-1321
Published	2021-07-14
Last modified	2026-06-17

Publisher (CNA): Mend · Vendor: putil-merge project

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

Am I affected?

Timeline

2021-07-14 11:15 UTCPublished CVE record published
2026-06-17 03:42 UTCUpdated Record last modified

putil-merge project putil-merge UPGRADE

Affected: >= 1.0.0 and <= 3.6.6

Fixed in: newer than 3.6.6

Safe to downgrade to: a release before 1.0.0

1. Check installed version

apt-cache policy putil-merge || rpm -q putil-merge || putil-merge --version

2. UPGRADE to newer than 3.6.6 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade putil-merge

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade putil-merge

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 1.0.0 (Debian / Ubuntu)

apt-cache madison putil-merge sudo apt install putil-merge=<VERSION_BEFORE_1.0.0> sudo apt-mark hold putil-merge

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

dnf --showduplicates list putil-merge sudo dnf downgrade putil-merge-<VERSION_BEFORE_1.0.0> sudo dnf versionlock add putil-merge

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-2021-25953?

putil-merge: upgrade to newer than 3.6.6. Exact commands for each OS are on this page.

Is CVE-2021-25953 being exploited?

CVE-2021-25953 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-2021-25953 affect?

CVE-2021-25953 affects putil-merge. Severity is critical (CVSS 9.8). Prototype pollution vulnerability in 'putil-merge' versions1.0.0 through 3.6.6 allows attacker to cause a denial of service and may lead to remote code execution.

How urgent is CVE-2021-25953?

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

Related CVEs

CVE-2021-23470 HIGH 8.2 UPGRADE This affects the package putil-merge before 3.8.0

References

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