CVE-2020-9493: A deserialization flaw was found in Apache Chainsaw versions prior to 2.1.0 which could lead to malicious code

Q: How do I fix CVE-2020-9493?

chainsaw: upgrade to 2.1.0; log4j: upgrade to 2.0; reload4j: upgrade to 1.2.18.1. Exact commands for each OS are on this page.

Q: Is CVE-2020-9493 being exploited?

CVE-2020-9493 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2020-9493 affect?

CVE-2020-9493 affects chainsaw, log4j, reload4j. Severity is critical (CVSS 9.8). A deserialization flaw was found in Apache Chainsaw versions prior to 2.1.0 which could lead to malicious code execution.

Q: How urgent is CVE-2020-9493?

Priority 67/100. Critical severity; EPSS top 8%: very likely to be exploited; Remotely exploitable, no login, no user action; On your watchlist

This week

CRITICAL 9.8REMOTEWATCHLISTUPGRADEUPGRADEUPGRADE

CVE-2020-9493 is a critical-severity flaw (CVSS 9.8) affecting chainsaw, log4j, reload4j. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A deserialization flaw was found in Apache Chainsaw versions prior to 2.1.0 which could lead to malicious code execution.

Why this priority

Critical severity
EPSS top 8%: very likely to be exploited
Remotely exploitable, no login, no user action
On your watchlist

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	4.6% (top 8%)
CISA exploited list	No
Weakness	CWE-502
Published	2021-06-16
Last modified	2026-10-07

Publisher (CNA): Apache Software Foundation · Vendor: apache · qos

Last updated 2026-10-07 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-06-16 08:15 UTCPublished CVE record published
2026-10-07 16:17 UTCUpdated Record last modified

apache chainsaw UPGRADE

Affected: < 2.1.0

Fixed in: 2.1.0

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 2.1.0 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade chainsaw

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

apache log4j UPGRADE

Affected: >= 1.2 and < 2.0

Fixed in: 2.0

Safe to downgrade to: a release before 1.2

1. Check installed version

apt-cache policy log4j || rpm -q log4j || log4j --version

2. UPGRADE to 2.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade log4j

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade log4j

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 1.2 (Debian / Ubuntu)

apt-cache madison log4j sudo apt install log4j=<VERSION_BEFORE_1.2> sudo apt-mark hold log4j

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

dnf --showduplicates list log4j sudo dnf downgrade log4j-<VERSION_BEFORE_1.2> sudo dnf versionlock add log4j

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.

qos reload4j UPGRADE

Affected: < 1.2.18.1

Fixed in: 1.2.18.1

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy reload4j || rpm -q reload4j || reload4j --version

2. UPGRADE to 1.2.18.1 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade reload4j

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade reload4j

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

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-2020-9493?

chainsaw: upgrade to 2.1.0; log4j: upgrade to 2.0; reload4j: upgrade to 1.2.18.1. Exact commands for each OS are on this page.

Is CVE-2020-9493 being exploited?

CVE-2020-9493 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-2020-9493 affect?

CVE-2020-9493 affects chainsaw, log4j, reload4j. Severity is critical (CVSS 9.8). A deserialization flaw was found in Apache Chainsaw versions prior to 2.1.0 which could lead to malicious code execution.

How urgent is CVE-2020-9493?

Priority 67/100. Critical severity; EPSS top 8%: very likely to be exploited; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Apache Log4j vulnerabilities

Related CVEs

CVE-2022-23307 HIGH 8.8 UPGRADE UPGRADE CVE-2020-9493 identified a deserialization issue that was present in Apache Chainsaw

References

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