CVE-2021-26505: Prototype pollution vulnerability in MrSwitch hello.js version 1.18.6, allows remote attackers to execute arbi

Q: How do I fix CVE-2021-26505?

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

Q: Is CVE-2021-26505 being exploited?

CVE-2021-26505 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-2021-26505 affect?

CVE-2021-26505 affects hello.js. Severity is critical (CVSS 9.8). Prototype pollution vulnerability in MrSwitch hello.js version 1.18.6, allows remote attackers to execute arbitrary code via hello.utils.extend function.

Q: How urgent is CVE-2021-26505?

Priority 56/100. Critical severity; Remotely exploitable, no login, no user action

This month

CRITICAL 9.8REMOTEDOWNGRADE

CVE-2021-26505 is a critical-severity flaw (CVSS 9.8) affecting hello.js. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Prototype pollution vulnerability in MrSwitch hello.js version 1.18.6, allows remote attackers to execute arbitrary code via hello.utils.extend function.

Why this priority

Critical severity
Remotely exploitable, no login, no user action

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

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.1% (top 33%)
CISA exploited list	No
Weakness	CWE-1321
Published	2023-08-11
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: hello.js project

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

Am I affected?

Timeline

2023-08-11 14:15 UTCPublished CVE record published
2026-06-17 03:43 UTCUpdated Record last modified

hello.js project hello.js DOWNGRADE

Affected: 1.18.6

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.18.6

1. Check installed version

npm ls hello.js

2. No fixed release: DOWNGRADE to a release before 1.18.6

npm view hello.js versions npm install hello.js@"<1.18.6"

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-2021-26505?

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

Is CVE-2021-26505 being exploited?

CVE-2021-26505 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-2021-26505 affect?

CVE-2021-26505 affects hello.js. Severity is critical (CVSS 9.8). Prototype pollution vulnerability in MrSwitch hello.js version 1.18.6, allows remote attackers to execute arbitrary code via hello.utils.extend function.

How urgent is CVE-2021-26505?

Priority 56/100. Critical severity; Remotely exploitable, no login, no user action

References

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