CVE-2021-43521: A Buffer Overflow vulnerability exists in zlog 1.2.15 via zlog_conf_build_with_file in src/zlog/src/conf.c.

This week

HIGH 7.5REMOTEDOWNGRADE

CVE-2021-43521 is a high-severity flaw (CVSS 7.5) affecting zlog. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A Buffer Overflow vulnerability exists in zlog 1.2.15 via zlog_conf_build_with_file in src/zlog/src/conf.c.

Why this priority

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

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.3% (top 30%)
CISA exploited list	No
Weakness	CWE-787
Published	2022-04-08
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: zlog project

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

Am I affected?

Timeline

2022-04-08 16:15 UTCPublished CVE record published
2026-06-17 04:11 UTCUpdated Record last modified

zlog project zlog DOWNGRADE

Affected: 1.2.15

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.2.15

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 1.2.15 (Debian / Ubuntu)

apt-cache madison zlog sudo apt install zlog=<VERSION_BEFORE_1.2.15> sudo apt-mark hold zlog

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list zlog sudo dnf downgrade zlog-<VERSION_BEFORE_1.2.15> sudo dnf versionlock add zlog

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-2021-43521?

zlog: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-43521 being exploited?

CVE-2021-43521 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-2021-43521 affect?

CVE-2021-43521 affects zlog. Severity is high (CVSS 7.5). A Buffer Overflow vulnerability exists in zlog 1.2.15 via zlog_conf_build_with_file in src/zlog/src/conf.c.

How urgent is CVE-2021-43521?

Priority 54/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

References

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