What is CVE-2021-39286?

CVE-2021-39286 is a medium-severity vulnerability in Webrecorder Pywb, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2021-08-18.

How severe is CVE-2021-39286?

Medium severity. CVSS v3 base score is 6.1 out of 10.

XSS in Webrecorder Pywb

CVE-2021-39286

Webrecorder pywb before 2.6.0 allows XSS because it does not ensure that Jinja2 templates are autoescaped.

Vulnerability class: XSS (Cross-Site Scripting)

Published 2021-08-18 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.007 (52.6th percentile), scored 2026-10-23.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 53rd percentile — 52.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.007 · newest: 0.007 · change: 0.000

Affected products

Webrecorder Pywb

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

References

github.com/webrecorder/pywb/commit/f7bd84cdacdd665ff73ae8d09a202f60be2ebae9 (Patch, Third Party Advisory)
github.com/webrecorder/pywb/compare/v-2.5.0...v-2.6.0 (Third Party Advisory, Release Notes)

Frequently asked questions

What is CVE-2021-39286?: CVE-2021-39286 is a medium-severity vulnerability in Webrecorder Pywb, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2021-08-18.
How severe is CVE-2021-39286?: Medium severity. CVSS v3 base score is 6.1 out of 10.