CVE-2021-26707: The merge-deep library before 3.0.3 for Node.js can be tricked into overwriting properties of Object.prototype

This month

CRITICAL 9.8REMOTEUPGRADEMITIGATE

CVE-2021-26707 is a critical-severity flaw (CVSS 9.8) affecting merge-deep, e-series performance analyzer. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

The merge-deep library before 3.0.3 for Node.js can be tricked into overwriting properties of Object.prototype or adding new properties to it. These properties are then inherited by every object in the program, thus facilitating prototype-pollution attacks against applications using this library.

Why this priority

Critical severity
Remotely exploitable, no login, no user action

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	1.9% (top 20%)
CISA exploited list	No
Weakness	CWE-1321
Published	2021-06-02
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: merge-deep project · netapp

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

Am I affected?

Timeline

2021-06-02 15:15 UTCPublished CVE record published
2026-06-17 03:43 UTCUpdated Record last modified

merge-deep project merge-deep UPGRADE

Affected: < 3.0.3

Fixed in: 3.0.3

Safe to downgrade to: no unaffected older release

1. Check installed version

npm ls merge-deep

2. UPGRADE to 3.0.3

npm install merge-deep@">=3.0.3"

netapp e-series performance analyzer MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy e-series-performance-analyzer || rpm -q e-series-performance-analyzer || e-series-performance-analyzer --version

No fixed or unaffected release known

Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.

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-2021-26707?

merge-deep: upgrade to 3.0.3; e-series performance analyzer: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-26707 being exploited?

CVE-2021-26707 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-2021-26707 affect?

CVE-2021-26707 affects merge-deep, e-series performance analyzer. Severity is critical (CVSS 9.8). The merge-deep library before 3.0.3 for Node.js can be tricked into overwriting properties of Object.prototype or adding new properties to it. These properties are then inherited by every object in the program, thus facilitating prototype-p

How urgent is CVE-2021-26707?

Priority 59/100. Critical severity; Remotely exploitable, no login, no user action

Software pages

Node.js vulnerabilities

Related CVEs

CVE-2018-3722 HIGH 8.8 UPGRADE merge-deep node module before 3.0.1 suffers from a Modification of Assumed-Immutable Data (MAID) vulnerability

References

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