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Fencer Vulns
medium 6.1

CVE-2023-51652 json

OWASP.AntiSamy mXSS when preserving comments

published 2024-01-02 2 y ago modified 2026-06-17 4 mo ago also GHSA-8x6f-956f-q43w , EUVD-2024-0305

cvss
6.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 39%
public exploits
0
none known

Summary

OWASP AntiSamy .NET is a library for performing cleansing of HTML coming from untrusted sources. Prior to version 1.2.0, there is a potential for a mutation cross-site scripting (mXSS) vulnerability in AntiSamy caused by flawed parsing of the HTML being sanitized. To be subject to this vulnerability the `preserveComments` directive must be enabled in your policy file and also allow for certain tags at the same time. As a result, certain crafty inputs can result in elements in comment tags being interpreted as executable when using AntiSamy's sanitized output. This is patched in OWASP AntiSamy .NET 1.2.0 and later. See important remediation details in the reference given below. As a workaround, manually edit the AntiSamy policy file (e.g., antisamy.xml) by deleting the `preserveComments` directive or setting its value to `false`, if present. Also it would be useful to make AntiSamy remove the `noscript` tag by adding a line described in the GitHub Security Advisory to the tag definitions under the `<tagrules>` node, or deleting it entirely if present. As the previously mentioned policy settings are preconditions for the mXSS attack to work, changing them as recommended should be sufficient to protect you against this vulnerability when using a vulnerable version of this library. However, the existing bug would still be present in AntiSamy or its parser dependency (HtmlAgilityPack). The safety of this workaround relies on configurations that may change in the future and don't address the root cause of the vulnerability. As such, it is strongly recommended to upgrade to a fixed version of AntiSamy.

Patch / fix

  • nuget OWASP.AntiSamy 1.2.0
  • spassarop owasp_antisamy_.net 1.2.0

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
2 y ago

Exploit prediction

0.45% chance of exploitation in the next 30 days, higher than 39% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
NVD 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/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
nuget OWASP.AntiSamy
<1.2.0
1.2.0

Affected products

  • spassarop antisamy-dotnet

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.