CVE-2026-57926: JetBrains YouTrack Prototype Pollution in Websandbox Bridge

Technical summary

The websandbox bridge in YouTrack fails to properly validate or sanitize object property assignments, allowing prototype pollution attacks. Prototype pollution occurs when an attacker manipulates an object's prototype chain to add or modify properties that affect application behavior. In this case, the vulnerability requires an authenticated user (PR:L), network access (AV:N), high attack complexity (AC:H), and user interaction (UI:R). The flaw is classified under CWE-1321 (Improperly Controlled Modification of Object-prototype Attributes in a JavaScript Object).

Business impact

The integrity impact is limited—modification of application properties could affect data consistency or behavior for the targeted user, but does not enable confidentiality breaches, denial of service, or unauthorized access to sensitive data. For most organizations, this represents a low-priority remediation item unless YouTrack is the central hub for project tracking and release coordination in a high-assurance environment.

Affected systems

JetBrains YouTrack installations running version 2026.2.16593 or later are patched. All earlier versions of the 2026.2 branch and prior major versions (2025.x, 2024.x, etc.) remain vulnerable. The vulnerability affects both on-premises and cloud-hosted deployments if running an unpatched build.

Exploitability

Exploitation is not trivial. An attacker must be an authenticated user of the YouTrack instance, possess sufficient access to trigger the websandbox bridge interaction, and convince or manipulate a user into performing a specific action (UI:R). Passive or automated exploitation is unlikely. The attack does not yield remote code execution or authentication bypass. There is no public exploit code reported, and this CVE is not tracked on the CISA KEV catalog.

Remediation

Upgrade YouTrack to version 2026.2.16593 or later. Organizations on earlier versions should consult the JetBrains security advisory and release notes to confirm the patch version in their release branch and plan a maintenance window. Verify against the vendor advisory for backport availability to older major versions if in-place upgrades are not feasible.

Patch guidance

Check your current YouTrack version via the Administration → System Information page. If running 2026.2.16592 or earlier, prioritize upgrade to 2026.2.16593 within your standard maintenance cycle. Organizations on extended support should verify patch availability for their branch. JetBrains typically publishes patch releases monthly; consult release.jetbrains.com/youtrack for the latest build.

Detection guidance

Monitor YouTrack logs for unusual property modifications or errors in the websandbox bridge. Look for suspicious patterns in request payloads targeting prototype or constructor properties if logging is configured at debug level. Network-level detection is difficult without application-layer instrumentation. Endpoint Detection & Response (EDR) solutions are unlikely to flag this activity as it occurs within an authenticated session and does not involve process execution or system calls.

Why prioritize this

This vulnerability merits low prioritization for most organizations due to its CVSS 2.6 score, requirement for authenticated access, high attack complexity, and user interaction dependency. Prioritize patching if YouTrack is mission-critical for release management or if your environment has a history of insider threats or compromised user accounts. Otherwise, fold the upgrade into regular maintenance schedules.

Risk score, explained

The CVSS score of 2.6 (Low) reflects the narrow threat model: an authenticated, low-privileged user must successfully trigger a specific interaction within the websandbox bridge (high complexity) and convince another user to participate (user interaction required). The impact is integrity-only with minimal scope—no confidentiality loss, no availability impact, and no cross-session effects. This profile is typical of logic flaws affecting single-user data consistency.

Frequently asked questions