CVE-2020-26293Public exploitNetwork attack vector

Cross-site scripting via unescaped CSS hex escapes

Published Jan 4, 2021 · Updated Aug 4, 2024

Cross-site scripting in Michael Ganss HtmlSanitizer before 5.0.372 allows remote attackers to inject script via crafted CSS. SanitizeStyleSheets serializes an allowed style element back into InnerHtml without escaping less-than characters recovered from CSS hexadecimal escapes, allowing a crafted closing style tag and event handler to survive sanitization. The style tag must be explicitly allowed, and script executes only when a consuming application renders the sanitized output in a user’s browser.

CVSS severity6.1
Medium
EPSS probability1.00%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in Michael Ganss HtmlSanitizer before 5.0.372 allows remote attackers to inject script via crafted CSS. SanitizeStyleSheets serializes an allowed style element back into InnerHtml without escaping less-than characters recovered from CSS hexadecimal escapes, allowing a crafted closing style tag and event handler to survive sanitization. The style tag must be explicitly allowed, and script executes only when a consuming application renders the sanitized output in a user’s browser.

The record

CVE
CVE-2020-26293
Published
Jan 4, 2021
Updated
Aug 4, 2024
Vendor
Michael Ganss
Product
HtmlSanitizer
Classifications
CWE-79, CWE-74, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 4, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 5.0.372

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Michael Ganss · HtmlSanitizerversion=< 5.0.372

Published CVSS scores

4.3NISTAV:N/AC:M/Au:N/C:N/I:P/A:N
6.1GitHub, Inc.CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:H/A:N
6.1NISTCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CWE-74Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')
T1203Exploitation for Client Execution

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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