CVE-2021-3377

ansi_up cross-site scripting vulnerability

6.1 MediumFix available

The npm package ansi_up converts ANSI escape codes into HTML. In ansi_up v4, ANSI escape codes can be used to create HTML hyperlinks. Due to insufficient URL sanitization, this feature is affected by a cross-site scripting (XSS) vulnerability. This issue is fixed in v5.0.0.

Attack profile

How easy it is to exploit

Attack vector: Network
Complexity: Low
Privileges needed: None
User interaction: Required

What an attacker can affect

Confidentiality: Low
Integrity: Low
Availability: None

Exploit likelihood

8.00%Up 7.4 points since Apr 14, 2021

What each source reports

NVD Score used 6.1

Record: CVE-2021-3377
CVSS 3.1: 6.1 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
CVSS 2.0: 4.3 MediumAV:N/AC:M/Au:N/C:N/I:P/A:N
Weakness: CWE-79
Updated: 2026-11-02

CVE List No score

Record: CVE-2021-3377
Updated: 2026-11-02

EUVDEUVD-2021-0589 No score

Record: EUVD-2021-0589
Updated: 2026-11-02

GitHub AdvisoriesGHSA-2v5f-23xc-v9qr 6.1

ansi_up cross-site scripting vulnerability

Record: GHSA-2v5f-23xc-v9qr
CVSS 3.1: 6.1 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Weakness: CWE-79
Updated: 2026-11-02

OSV 6.1

Record: CVE-2021-3377
CVSS 3.1: 6.1 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Updated: 2026-11-02

OSVDEBIAN-CVE-2021-3377 6.1

Record: DEBIAN-CVE-2021-3377
CVSS 3.1: 6.1 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Updated: 2026-11-02

OSVGHSA-2v5f-23xc-v9qr 6.1

ansi_up cross-site scripting vulnerability

Record: GHSA-2v5f-23xc-v9qr
CVSS 3.1: 6.1 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Weakness: CWE-79
Updated: 2026-11-02

OSVUBUNTU-CVE-2021-3377 6.1

Record: UBUNTU-CVE-2021-3377
CVSS 3.1: 6.1 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Updated: 2026-11-02

Affected products

ansi up project up

Affected packages

Affected packages
Package	Affected	Fixed
`ansi_up` npm	before 5.0.0	5.0.0
`node-ansi-up` Debian:12	before 5.0.0+dfsg-1	5.0.0+dfsg-1
`node-ansi-up` Debian:13	before 5.0.0+dfsg-1	5.0.0+dfsg-1
`node-ansi-up` Debian:14	before 5.0.0+dfsg-1	5.0.0+dfsg-1
`node-ansi-up` Ubuntu:20.04:LTS	All versions, plus listed versions 4.0.3+dfsg-2	None known
`node-ansi-up` Ubuntu:22.04:LTS	All versions, plus listed versions 5.0.0+dfsg-15.1.0+dfsg-1	None known

Public exploits

Links only. Every CVE stores no exploit code.

Public exploits
Source	Link	Date
Nuclei	npm ansi_up v4 - Cross-Site Scripting

History

History
Recorded	Changed	Sources
Nov 2, 2026	first indexed	CVE List, EUVD, GitHub Advisories, Nuclei, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-3377 is a medium vulnerability (CVSS 6.1) in Ansi Up Project Up, published March 5, 2021. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 8.00%, the 94th percentile. Fixed in ansi_up 5.0.0.