Authorization Bypass Enables Admin Escalation and Attachment Theft

Vikunja before 2.2.1 contains an authorization flaw where the LinkSharing.ReadAll endpoint exposes share hashes to users with read access, enabling permission escalation to admin-level shares. The GetTaskAttachment endpoint performs permission checks against user-supplied task IDs but fetches attachments by sequential ID without verifying ownership, allowing attackers to download and delete all file attachments across all projects instance-wide.

Casky was already ahead

This CVE exploits attack patterns that Casky's 283matched 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

Vikunja versions before 2.2.1 suffer from multiple authorization flaws that cascade into severe privilege escalation and data exfiltration vulnerabilities. The LinkSharing.ReadAll endpoint carelessly exposes share hashes to any user with read access, allowing attackers to discover and escalate to admin-level shares they shouldn't access. Simultaneously, the GetTaskAttachment endpoint validates permissions against user-supplied task IDs but retrieves attachments by sequential ID without ownership verification—enabling instance-wide file enumeration and deletion across all projects. With a CVSS score of 9.8, this vulnerability affects any organization deploying Vikunja, from small teams to enterprises, turning legitimate read-access users into attackers capable of lateral movement and destructive operations.

Casky's 283 matched skills detect the attack patterns underlying this CVE by analyzing MITRE techniques TA0004 (Privilege Escalation) and TA0006 (Credential Access). Practitioners using Casky's Claude-powered analysis would observe: (1) Privilege Escalation signals when share hash enumeration succeeds, revealing admin-level shares accessible to low-privileged accounts; (2) Credential Access patterns when sequential attachment ID requests return files outside the user's project scope, indicating broken access controls; (3) Authorization bypass anomalies in API response metadata and error handling that expose system structure. The platform's extended reasoning identifies the root cause—permission checks decoupled from data retrieval operations—and maps defensive gaps to specific skill areas covering API authorization testing, object-level access control validation, and enumeration resistance.

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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 →

283 Casky skills cover this attack pattern

These skills use Claude AI's reasoning model to surface findings in the same attack categories as CVE-2026-56765.

abusing-dpapi-for-credential-access

red teaming · high

Run

abusing-shadow-credentials-for-privesc

red teaming · high

Run

Access with Stolen Session Cookie

identity access management · low

Run

MITRE ATT&CK Techniques

TA0004 TA0006

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