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CVE Record

CVE-2021-35043: OWASP AntiSamy before 1.6.4 allows XSS via HTML attributes when using the HTML output serializer (XHTML is...

OWASP AntiSamy before 1.6.4 allows XSS via HTML attributes when using the HTML output serializer (XHTML is not affected). This was demonstrated by a javascript: URL with &#00058 as the replacement for the : character.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2021-35043 is a cross-site scripting flaw in OWASP AntiSamy before 1.6.4. Applications relying on AntiSamy to clean user-supplied HTML could still emit unsafe HTML attributes when using the HTML output serializer. XHTML output is described as not affected.

Executive priority

Prioritize remediation for internet-facing applications that accept or display rich user-controlled HTML. The known evidence supports moderate urgency: XSS impact can be material, but the bundle provides no CVSS score or active exploitation evidence.

Technical view

The issue is an HTML serializer sanitization bypass in OWASP AntiSamy versions before 1.6.4. The CVE description says unsafe HTML attributes could survive normalization through encoded character handling. The provided record has no CVSS, CWE, or detailed affected CPE data.

Likely exposure

Exposure is most likely in web applications or downstream products that include OWASP AntiSamy before 1.6.4 and sanitize untrusted HTML using the HTML output serializer. The bundle does not identify exact affected applications, package coordinates, or Oracle product names.

Exploitation context

The CVE describes a demonstrated XSS condition, but the bundle does not cite active exploitation and KEV is false. Treat this as a sanitizer-bypass risk where stored user content, comments, rich-text fields, or profile HTML could become an execution path.

Researcher notes

The public record is sparse. Key points are AntiSamy before 1.6.4, HTML serializer only, XHTML not affected, and a fix associated with the 1.6.4 release and GitHub PR 87. Avoid extrapolating affected downstream products without vendor-specific confirmation.

Mitigation direction

  • Upgrade OWASP AntiSamy to version 1.6.4 or later.
  • Apply vendor updates for bundled AntiSamy dependencies.
  • Review Oracle CPU guidance if using affected Oracle products.
  • Prefer vendor-documented mitigations where direct upgrades are not possible.
  • Retest HTML sanitization paths after dependency changes.

Validation and detection

  • Inventory direct and transitive OWASP AntiSamy versions.
  • Identify uses of the HTML output serializer for untrusted content.
  • Confirm XHTML serializer paths are not misclassified as HTML paths.
  • Run safe regression tests for attribute sanitization behavior.
  • Verify deployed artifacts include AntiSamy 1.6.4 or later.
Prepared
Confidence
medium
Sources
8

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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CVE-2021-35043 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
0Timeline events
0ADP providers
7Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/an/an/aListed
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.