CVE-2020-15366: An issue was discovered in ajv.validate() in Ajv (aka Another JSON Schema Validator) 6.12.2

This month

MEDIUM 5.6REMOTEDOWNGRADE

CVE-2020-15366 is a medium-severity flaw (CVSS 5.6) affecting ajv. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

An issue was discovered in ajv.validate() in Ajv (aka Another JSON Schema Validator) 6.12.2. A carefully crafted JSON schema could be provided that allows execution of other code by prototype pollution. (While untrusted schemas are recommended against, the worst case of an untrusted schema should be a denial of service, not execution of code.)

Why this priority

Remotely exploitable, no login, no user action

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

Risk facts

CVSS score	5.6 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	2.3% (top 17%)
CISA exploited list	No
Weakness	CWE-1321
Published	2020-07-15
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: ajv.js

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

Am I affected?

Timeline

2020-07-15 20:15 UTCPublished CVE record published
2026-06-17 02:56 UTCUpdated Record last modified

ajv.js ajv DOWNGRADE

Affected: 6.12.2

Fixed in: no fixed release known

Safe to downgrade to: a release before 6.12.2

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 6.12.2 (Debian / Ubuntu)

apt-cache madison ajv sudo apt install ajv=<VERSION_BEFORE_6.12.2> sudo apt-mark hold ajv

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

dnf --showduplicates list ajv sudo dnf downgrade ajv-<VERSION_BEFORE_6.12.2> sudo dnf versionlock add ajv

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-2020-15366?

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

Is CVE-2020-15366 being exploited?

CVE-2020-15366 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-2020-15366 affect?

CVE-2020-15366 affects ajv. Severity is medium (CVSS 5.6). An issue was discovered in ajv.validate() in Ajv (aka Another JSON Schema Validator) 6.12.2. A carefully crafted JSON schema could be provided that allows execution of other code by prototype pollution. (While untrusted schemas are recommen

How urgent is CVE-2020-15366?

Priority 45/100. Remotely exploitable, no login, no user action

References

← Back to latest CVEs