CVE-2021-20085: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution') in backbone-query-pa

This month

HIGH 8.8DOWNGRADE

CVE-2021-20085 is a high-severity flaw (CVSS 8.8) affecting backbone-query-parameters. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution') in backbone-query-parameters 0.4.0 allows a malicious user to inject properties into Object.prototype.

Why this priority

High severity
Public exploit reference

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

Risk facts

CVSS score	8.8 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	1.6% (top 24%)
CISA exploited list	No
Weakness	CWE-1321
Published	2021-04-23
Last modified	2026-06-17

Publisher (CNA): Tenable Network Security, Inc. · Vendor: backbone-query-parameters project

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

Am I affected?

Timeline

2021-04-23 19:15 UTCPublished CVE record published
2026-06-17 03:33 UTCUpdated Record last modified

backbone-query-parameters project backbone-query-parameters DOWNGRADE

Affected: 0.4.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 0.4.0

1. Check installed version

apt-cache policy backbone-query-parameters || rpm -q backbone-query-parameters || backbone-query-parameters --version

2. No fixed release: DOWNGRADE to a release before 0.4.0 (Debian / Ubuntu)

apt-cache madison backbone-query-parameters sudo apt install backbone-query-parameters=<VERSION_BEFORE_0.4.0> sudo apt-mark hold backbone-query-parameters

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

dnf --showduplicates list backbone-query-parameters sudo dnf downgrade backbone-query-parameters-<VERSION_BEFORE_0.4.0> sudo dnf versionlock add backbone-query-parameters

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-2021-20085?

backbone-query-parameters: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-20085 being exploited?

CVE-2021-20085 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-2021-20085 affect?

CVE-2021-20085 affects backbone-query-parameters. Severity is high (CVSS 8.8). Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution') in backbone-query-parameters 0.4.0 allows a malicious user to inject properties into Object.prototype.

How urgent is CVE-2021-20085?

Priority 55/100. High severity; Public exploit reference

References

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