CVE-2021-36770: Encode.pm, as distributed in Perl through 5.34.0, allows local users to gain privileges via a Trojan horse Enc

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HIGH 7.8UPGRADEMITIGATE

CVE-2021-36770 is a high-severity flaw (CVSS 7.8) affecting p5-encode, fedora. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Encode.pm, as distributed in Perl through 5.34.0, allows local users to gain privileges via a Trojan horse Encode::ConfigLocal library (in the current working directory) that preempts dynamic module loading. Exploitation requires an unusual configuration, and certain 2021 versions of Encode.pm (3.05 through 3.11). This issue occurs because the || operator evaluates @INC in a scalar context, and thus @INC has only an integer value.

Why this priority

High severity

A fixed release or distro patch exists.

Risk facts

CVSS score	7.8 (High)
Attack vector	Local
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	1.4% (top 28%)
CISA exploited list	No
Weakness	CWE-427
Published	2021-08-11
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: fedoraproject · p5-encode project

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

Am I affected?

Timeline

2021-08-11 23:15 UTCPublished CVE record published
2026-06-17 03:59 UTCUpdated Record last modified

p5-encode project p5-encode UPGRADE

Affected: >= 3.05 and < 3.12

Fixed in: 3.12

Safe to downgrade to: a release before 3.05

1. Check installed version

apt-cache policy p5-encode || rpm -q p5-encode || p5-encode --version

2. UPGRADE to 3.12 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade p5-encode

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade p5-encode

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 3.05 (Debian / Ubuntu)

apt-cache madison p5-encode sudo apt install p5-encode=<VERSION_BEFORE_3.05> sudo apt-mark hold p5-encode

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

dnf --showduplicates list p5-encode sudo dnf downgrade p5-encode-<VERSION_BEFORE_3.05> sudo dnf versionlock add p5-encode

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 · 33

Fixed in: no fixed release known

Safe to downgrade to: a release before 33

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-2021-36770?

p5-encode: upgrade to 3.12; fedora: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-36770 being exploited?

CVE-2021-36770 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-2021-36770 affect?

CVE-2021-36770 affects p5-encode, fedora. Severity is high (CVSS 7.8). Encode.pm, as distributed in Perl through 5.34.0, allows local users to gain privileges via a Trojan horse Encode::ConfigLocal library (in the current working directory) that preempts dynamic module loading. Exploitation requires an unusual

How urgent is CVE-2021-36770?

Priority 45/100. High severity

Software pages

Perl vulnerabilities

References

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