CVE-2021-36377: Fossil before 2.14.2 and 2.15.x before 2.15.2 often skips the hostname check during TLS certificate validation

This month

HIGH 7.5REMOTEUPGRADEMITIGATE

CVE-2021-36377 is a high-severity flaw (CVSS 7.5) affecting fossil, fedora. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Fossil before 2.14.2 and 2.15.x before 2.15.2 often skips the hostname check during TLS certificate validation.

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.6% (top 53%)
CISA exploited list	No
Weakness	CWE-295
Published	2021-07-12
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: fedoraproject · fossil-scm

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

Am I affected?

Timeline

2021-07-12 13:15 UTCPublished CVE record published
2026-06-17 03:58 UTCUpdated Record last modified

fossil-scm fossil UPGRADE

Affected: < 2.14.2 · >= 2.15.0 and < 2.15.2

Fixed in: 2.14.2, 2.15.2

Safe to downgrade to: a release before 2.15.0

1. Check installed version

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

2. UPGRADE to 2.14.2 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade fossil

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade fossil

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 2.15.0 (Debian / Ubuntu)

apt-cache madison fossil sudo apt install fossil=<VERSION_BEFORE_2.15.0> sudo apt-mark hold fossil

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

dnf --showduplicates list fossil sudo dnf downgrade fossil-<VERSION_BEFORE_2.15.0> sudo dnf versionlock add fossil

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.

fedoraproject fedora MITIGATE

Affected: 34

Fixed in: no fixed release known

Safe to downgrade to: a release before 34

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

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-2021-36377?

fossil: upgrade to 2.14.2, 2.15.2; fedora: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-36377 being exploited?

CVE-2021-36377 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-2021-36377 affect?

CVE-2021-36377 affects fossil, fedora. Severity is high (CVSS 7.5). Fossil before 2.14.2 and 2.15.x before 2.15.2 often skips the hostname check during TLS certificate validation.

How urgent is CVE-2021-36377?

Priority 43/100. High severity; Remotely exploitable, no login, no user action

Related CVEs

CVE-2022-34009 MEDIUM 5.5 DOWNGRADE Fossil 2.18 on Windows allows attackers to cause a denial of service (daemon crash) via an XSS payload in a ti

References

← Back to latest CVEs