Vulnerability in HTMLSanitizer (CVE-2025-52561)

Summary

Vulnerability in HTMLSanitizer (CVE-2025-52561). Risk of unauthorized operations or information disclosure. Exploitable via svg. Mitigation: upgrade to 0.2.1 or later.

Original description

The description as published by the source.

Description

When adding the style tag to the whitelist, content inside the tag is incorrectly unescaped, and closing tags injected as content are interpreted as real HTML, enabling tag injection and JavaScript execution.

This behavior is similar to the sanitization bypass described in CVE-2020-4054 (Sanitize for Ruby).

using HTMLSanitizer

user_input = "&lt;/style>&lt;img src onerror=alert(1)>"

whitelist = deepcopy(HTMLSanitizer.WHITELIST)
append!(whitelist[:elements], ["style"])
result = sanitize(user_input, whitelist=whitelist)
print(result) #

Impact

Possible XSS in any HTML that is sanitized with this library.

Patches

Users should upgrade to v0.2.1 as soon as possible. In this version, svg and math tags are removed by default.

Workarounds

Add the math and svg elements to your whitelist manually via e.g.

whitelist = deepcopy(HTMLSanitizer.WHITELIST)
append!(whitelist[:removed_elements], ["math", "svg"])

and pass this modified whitelist to sanitize:

sanitize(user_input, whitelist=whitelist)

References

PR for fix

Credits

Thanks to Chen T for finding and reporting this issue.

Source: OSV.dev (Open Source Vulnerabilities) NVD GitHub Advisory OSV

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2025-52561 has been found in HTMLSanitizer.
Attackers can target a specific entry point like svg over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: upgrade HTMLSanitizer to 0.2.1 or later.
If unsure, ask your IT team or search "HTMLSanitizer CVE-2025-52561" on the vendor's site.

CVE-2025-52561 (HTMLSanitizer)
Attack surface: svg / math / sanitize
Patched: 0.2.1 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (unclassified) exists in HTMLSanitizer. Attackers reach the vulnerable code path via svg.

📍 Affected scope

Check the vendor advisory for the affected versions of HTMLSanitizer. Attack surface: svg / math / sanitize.

🔥 Severity

Severity: ?. Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 0.2.1.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'HTMLSanitizer' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

1
Identify exposure identify
```
grep -r 'HTMLSanitizer' . | grep -v node_modules
```
リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で HTMLSanitizer を grep し、稼働しているサービス・バージョンを把握する。
2
Apply patch patch
```
Upgrade HTMLSanitizer to 0.2.1
```
ステージング環境で 0.2.1 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
3
Post-deployment verification verify
```
Confirm patched version is live in production
```
パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

Julia HTMLSanitizer

[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"0.2.1"}]}]