CVE-2020-26956

MEDIUMNVD 6.16.1

6.1

In some cases, removing HTML elements during sanitization would keep existing SVG event handlers and therefore lead to XSS. This vulnerability affects Firefox < 83, Firefox ESR < 78.5, and Thunderbird < 78.5.

CVSS v3: 6.1
EG Score: 6.1(low)
EPSS: 56.3%
KEV: Not listed

Published

December 9, 2020

Last Modified

November 21, 2024

References (8)

security@mozillahttps://bugzilla.mozilla.org/show_bug.cgi?id=1666300
security@mozillahttps://www.mozilla.org/security/advisories/mfsa2020-50/
security@mozillahttps://www.mozilla.org/security/advisories/mfsa2020-51/
security@mozillahttps://www.mozilla.org/security/advisories/mfsa2020-52/
af854a3a-2127-422b-91ae-364da2661108https://bugzilla.mozilla.org/show_bug.cgi?id=1666300
af854a3a-2127-422b-91ae-364da2661108https://www.mozilla.org/security/advisories/mfsa2020-50/
af854a3a-2127-422b-91ae-364da2661108https://www.mozilla.org/security/advisories/mfsa2020-51/
af854a3a-2127-422b-91ae-364da2661108https://www.mozilla.org/security/advisories/mfsa2020-52/

Patch Availability(15)

Vendor / Ecosystem	Fixed in / Patch	Released	Source
ubuntu	firefox-mozsymbols (83.0+build2-0ubuntu0.16.04.3) @ xenial	2026-05-23	ubuntu
ubuntu	xul-ext-lightning (1:78.5.0+build3-0ubuntu0.20.10.1) @ groovy	2026-05-23	ubuntu
ubuntu	firefox-mozsymbols (83.0+build2-0ubuntu0.20.10.1) @ groovy	2026-05-23	ubuntu
redhat	firefox-0:78.5.0-1.el8_0	2020-12-01	redhat
redhat	thunderbird-0:78.5.0-1.el8_0	2020-11-30	redhat
redhat	thunderbird-0:78.5.0-1.el7_9	2020-11-30	redhat
redhat	firefox-0:78.5.0-1.el7_9	2020-11-30	redhat
redhat	thunderbird-0:78.5.0-1.el6_10	2020-11-30	redhat
redhat	thunderbird-0:78.5.0-1.el8_3	2020-11-30	redhat
redhat	firefox-0:78.5.0-1.el8_1	2020-11-30	redhat
redhat	thunderbird-0:78.5.0-1.el8_1	2020-11-30	redhat
redhat	firefox-0:78.5.0-1.el8_3	2020-11-30	redhat
redhat	firefox-0:78.5.0-1.el6_10	2020-11-30	redhat
redhat	firefox-0:78.5.0-1.el8_2	2020-11-30	redhat
redhat	thunderbird-0:78.5.0-1.el8_2	2020-11-30	redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

CWE-79Cross-site Scripting (XSS)

All Vendor Advisories

(15)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 13× in last 7d / 20× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

2026-06-08 14:15 UTCEPSS rescore
2026-06-07 15:23 UTCEPSS rescore
2026-06-07 15:23 UTCEPSS rescore
2026-06-07 15:23 UTCEPSS rescore
2026-06-07 11:59 UTCOSV refresh
2026-06-06 13:46 UTCEPSS rescore
2026-06-06 13:45 UTCEPSS rescore
2026-06-05 22:45 UTCEPSS rescore
2026-06-05 22:45 UTCEPSS rescore
2026-06-05 06:08 UTCEPSS rescore
2026-06-05 06:08 UTCEPSS rescore
2026-06-04 13:10 UTCEPSS rescore
2026-06-04 13:10 UTCEPSS rescore
2026-06-02 20:11 UTCEPSS rescore
2026-06-02 20:11 UTCEPSS rescore
2026-06-01 13:50 UTCEPSS rescore
2026-05-31 22:29 UTCEPSS rescore
2026-05-31 22:29 UTCEPSS rescore
2026-05-31 00:15 UTCEPSS rescore
2026-05-31 00:15 UTCEPSS rescore

Frequently asked(5)

What is CVE-2020-26956?

CVE-2020-26956 is a medium vulnerability published on December 9, 2020. In some cases, removing HTML elements during sanitization would keep existing SVG event handlers and therefore lead to XSS. This vulnerability affects Firefox < 83, Firefox ESR < 78.5, and Thunderbird < 78.5.

When was CVE-2020-26956 disclosed?

CVE-2020-26956 was first published in the National Vulnerability Database on December 9, 2020, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.

Is CVE-2020-26956 actively exploited?

CVE-2020-26956 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 56.3% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.

What is the CVSS score of CVE-2020-26956?

CVE-2020-26956 has a CVSS v3 base score of 6.1 (NVD). The EG score is currently aggregating — additional source signals are being incorporated as they become available..

How do I remediate CVE-2020-26956?

Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2020-26956, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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CVE-2020-26956

Published

Last Modified

References (8)

Patch Availability(15)

Weakness Classification(1)

All Vendor Advisories

Data Freshness Timeline

Frequently asked(5)

Dependency Blast Radius

Is Your Infrastructure Affected by CVE-2020-26956?

Same vendor

Same CWE

CVE-2020-26956

📅 Published

🔄 Last Modified

🔗 References (8)

Patch Availability(15)

Weakness Classification(1)

All Vendor Advisories

Data Freshness Timeline

❓ Frequently asked(5)

Dependency Blast Radius

Is Your Infrastructure Affected by CVE-2020-26956?

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References (8)

Frequently asked(5)

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