CVE-2021-43307: An exponential ReDoS (Regular Expression Denial of Service) can be triggered in the semver-regex npm package,

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MEDIUM 5.9REMOTEUPGRADE

CVE-2021-43307 is a medium-severity flaw (CVSS 5.9) affecting semver-regex. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

An exponential ReDoS (Regular Expression Denial of Service) can be triggered in the semver-regex npm package, when an attacker is able to supply arbitrary input to the test() method

Why this priority

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

A fixed release or distro patch exists.

Risk facts

CVSS score	5.9 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	1.6% (top 25%)
CISA exploited list	No
Weakness	CWE-1333
Published	2022-06-02
Last modified	2026-06-17

Publisher (CNA): JFrog · Vendor: semver-regex project

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

Am I affected?

Timeline

2022-06-02 14:15 UTCPublished CVE record published
2026-06-17 04:10 UTCUpdated Record last modified

semver-regex project semver-regex UPGRADE

Affected: < 3.1.4 · >= 4.0.0 and < 4.0.3

Fixed in: 3.1.4, 4.0.3

Safe to downgrade to: a release before 4.0.0

1. Check installed version

apt-cache policy semver-regex || rpm -q semver-regex || semver-regex --version

2. UPGRADE to 3.1.4 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade semver-regex

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade semver-regex

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 4.0.0 (Debian / Ubuntu)

apt-cache madison semver-regex sudo apt install semver-regex=<VERSION_BEFORE_4.0.0> sudo apt-mark hold semver-regex

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

dnf --showduplicates list semver-regex sudo dnf downgrade semver-regex-<VERSION_BEFORE_4.0.0> sudo dnf versionlock add semver-regex

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-2021-43307?

semver-regex: upgrade to 3.1.4, 4.0.3. Exact commands for each OS are on this page.

Is CVE-2021-43307 being exploited?

CVE-2021-43307 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-2021-43307 affect?

CVE-2021-43307 affects semver-regex. Severity is medium (CVSS 5.9). An exponential ReDoS (Regular Expression Denial of Service) can be triggered in the semver-regex npm package, when an attacker is able to supply arbitrary input to the test() method

How urgent is CVE-2021-43307?

Priority 49/100. Public exploit reference; Remotely exploitable, no login, no user action

Software pages

npm packages vulnerabilities

Related CVEs

CVE-2021-3795 HIGH 7.5 UPGRADE semver-regex is vulnerable to Inefficient Regular Expression Complexity

References

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