How severe is CVE-2026-3455?

No CVSS score has been assigned to CVE-2026-3455 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-3455?

CVE-2026-3455 affects the following packages: mailparser (npm). Ecosystems affected: npm.

How do I fix CVE-2026-3455?

Update mailparser to 3.9.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-3455 is resolved across your whole dependency graph.

How do I detect CVE-2026-3455 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mailparser, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-3455 if there is no patch (or I can't update yet)?

Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Is CVE-2026-3455 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-3455 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-3455?

CVE-2026-3455 has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 30th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-3455?

CVE-2026-3455 is classified as Cross-site Scripting (XSS) (CWE-79). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2026-3455 published, and has it been updated?

CVE-2026-3455 was published on March 3, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

CVE-2026-3455: mailparser XSS

Exploitation Status

Proof-of-concept exploit code exists

CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-3455.

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs30th percentile — riskier than 30% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

1Kother npm packages depend on this — each one inherits the vulnerability until it's patched upstream

mailparsernpm

7.9Mdownloads / week

Description

Versions of the package mailparser before 3.9.3 are vulnerable to Cross-site Scripting (XSS) via the textToHtml() function due to the improper sanitisation of URLs in the email content. An attacker can execute arbitrary scripts in victim browsers by adding extra quote " to the URL with embedded malicious JavaScript code.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`mailparser`	all versions	3.9.3`npm install mailparser@3.9.3`

Affected Products

1 product · 1 configurations

Application

mailparsernodemailer

< 3.9.3

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mailparser, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update mailparser to 3.9.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-3455 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Frequently Asked Questions

Versions of the package mailparser before 3.9.3 are vulnerable to Cross-site Scripting (XSS) via the textToHtml() function due to the improper sanitisation of URLs in the email content. An attacker can execute arbitrary scripts in victim browsers by adding extra quote " to the URL with embedded malicious JavaScript code.

O3 Security · Impact-Aware SCA

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CVE-2026-3455 — mailparser