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Fencer Vulns
medium 6.1

CVE-2021-3377 json

ansi_up cross-site scripting vulnerability

published 2021-03-05 5 y ago modified 2026-06-17 4 mo ago also GHSA-2v5f-23xc-v9qr , EUVD-2021-0589

cvss
6.1
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
8.0%
EPSS 8.0% chance of exploitation in 30 days, percentile 94%
public exploits
0
none known, plus a Nuclei check

Summary

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.

Patch / fix

  • npm ansi_up 5.0.0
  • ansi_up_project ansi_up 5.0.0
  • node-ansi-up Debian 14, Debian 13, Debian 12 5.0.0+dfsg-1

debian advisories DEBIAN-CVE-2021-3377

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-3377 updated cvss 4.6

nodejs-ansi_up: XSS due to insufficient URL sanitization

  • Red Hat Advanced Cluster Management for Kubernetes 2 kui-web-terminal-rhel8
    affected: no fix available

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

8.00% chance of exploitation in the next 30 days, higher than 94% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • Nuclei template npm ansi_up v4 - Cross-Site Scripting nuclei detection template
  • doyensec.com https://doyensec.com/resources/Doyensec_Advisory_ansi_up4_XSS.pdf referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
NVD 2.0 4.3 AV:N/AC:M/Au:N/C:N/I:P/A:N
GitHub 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Affected packages

ecosystem package affected fixed in
npm ansi_up
<5.0.0
5.0.0

Classification

Weakness
  • CWE-79 Improper Neutralization of Input During Web Page Generation

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.