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Critical

Stored XSS sanitizer bypass in sanitize-html via disallowed xmp elements

IdentifiersCVE-2026-44990CWE-79· Improper Neutralization of Input…

CVE-2026-44990 is a sanitizer bypass in sanitize-html affecting versions prior to 2.17.4 under the default configuration. In the default disallowedTagsMode: 'discard' path, attacker-controlled content placed inside a disallowed xmp element can be transformed into live HTML or JavaScript instead of being safely neutralized. Applications such as ApostropheCMS, or any application using sanitize-html to process untrusted HTML and then render the sanitized output back to users, may therefore expose a stored cross-site scripting condition. The provided content indicates the issue is fixed in sanitize-html 2.17.4. There is also mention of an unconfirmed report suggesting the bug may have been introduced specifically in 2.17.3, but the supplied advisory text states affected versions are all versions prior to 2.17.4.

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation can result in stored XSS. An attacker able to submit crafted HTML content can cause arbitrary JavaScript to execute in the browsers of other users who later view the sanitized and rendered content. This can enable session theft, credential capture, unauthorized actions in the victim's session, content manipulation, and access to sensitive data available to the victim in the application context. The supplied CVSS context indicates no direct availability impact, but high confidentiality and integrity impact with scope change.

Mitigation

If you can’t patch tonight, do this now.

If immediate patching is not possible, do not rely on the default sanitize-html handling of untrusted HTML containing xmp. Pre-filter input to reject or strip xmp tags and their contents before sanitization, or configure sanitization logic to fully remove dangerous container elements rather than discarding only the tag wrapper. Additionally, avoid rendering sanitized output as trusted HTML unless necessary, and apply context-appropriate output encoding or additional validation where feasible.

Remediation

Patch, then assume compromise.

Upgrade sanitize-html to version 2.17.4 or later, which patches the sanitizer bypass. Review any dependency trees, including applications such as ApostropheCMS deployments, to ensure the vulnerable sanitize-html version is not retained transitively. After upgrading, validate that sanitization behavior for disallowed raw-text-like elements such as xmp matches security expectations.
PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType
ApostrophecmsSanitize-Htmlapplication

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

8 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.

8 SOURCESView more in app
What this page doesn’t show

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Exposure mapping

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Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity7

Community discussion across Reddit, Mastodon, and other social sources.

EXTERNAL REFERENCES
MITRE CVE
cve.org · CVE-2026-44990
NVD
nvd.nist.gov/vuln/detail/CVE-2026-44990
MITRE CWE · CWE-79
Improper Neutralization of Input During Web…
github.com
github.com/apostrophecms/apostrophe/security/advisories/GHSA-rpr9-rxv7-x643