Stored XSS via SVG Upload in OAuth Profile Images

Open WebUI before 0.9.5 contains a stored cross-site scripting vulnerability in the OAuth authentication flow where the picture claim URL MIME type is inferred from file extension rather than Content-Type header, allowing SVG files to bypass the profile image validator and be stored as data URIs. Authenticated users who visit the profile image endpoint receive attacker-controlled SVG content with inline disposition and no default security headers, enabling script execution in the same origin to steal authentication tokens and achieve account takeover.

Casky was already ahead

This CVE exploits attack patterns that Casky's 322matched skills already investigate — long before this vulnerability was disclosed. Claude's reasoning model maps these techniques to MITRE ATT&CK, so practitioners who ran these skills have already seen the threat behaviour in their findings.

Analysis

Open WebUI versions prior to 0.9.5 contain a stored cross-site scripting vulnerability in the OAuth authentication flow that allows attackers to inject malicious SVG files as profile images. The vulnerability stems from improper input validation where the application infers file types from extensions rather than respecting Content-Type headers, enabling SVG files containing executable scripts to bypass security checks. These malicious SVGs are then stored as data URIs and served to authenticated users without proper security headers or content disposition restrictions. Any organization using Open WebUI for authentication and access control is affected, particularly those relying on OAuth for identity management where attackers can compromise user accounts or inject payloads that execute in the application's origin context.

Casky's 322 matching skills map directly to MITRE ATT&CK techniques TA0001 (Reconnaissance) and TA0043 (Reconnaissance), enabling practitioners to detect the attack chain through multiple vectors. When analyzing findings, practitioners would identify CWE-20 (Improper Input Validation) patterns where the system fails to validate file type integrity—a critical detection point where Claude's extended reasoning correlates MIME type mismatches against stored profile data. Security teams would see anomalies in OAuth claim processing, unexpected SVG content in user profile endpoints, and data URI schemes bypassing Content-Type enforcement. Casky's skills help practitioners distinguish between legitimate profile image uploads and weaponized SVG payloads by analyzing the relationship between file extension claims, actual content headers, and execution context—revealing the reconnaissance and initial access tactics used to establish persistent XSS in the application.

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Casky Risk Score

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EPSS Probability

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Shodan Exposure

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GreyNoise Signal

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Composite risk scoring from EPSS, CISA KEV, Shodan, and GreyNoise — 21 security APIs correlated into a single Casky Risk Score. Coming in Casky Pro. Join early access →

322 Casky skills cover this attack pattern

These skills use Claude AI's reasoning model to surface findings in the same attack categories as CVE-2026-56398.

Abuse of Public-Facing API: Mobile API Abuse

mobile security · low

Run

abusing-dpapi-for-credential-access

red teaming · high

Run

abusing-shadow-credentials-for-privesc

red teaming · high

Run

MITRE ATT&CK Techniques

TA0001 TA0043

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