CVE-2026-49383: IntelliJ IDEA UI Designer XML External Entity (XXE) Information Disclosure

Technical summary

This vulnerability exists in IntelliJ IDEA's UI Designer component, which parses form definition files. The flaw falls under CWE-611 (Improper Restriction of XML External Entity Reference), a class of vulnerability that arises when XML parsers process untrusted input without properly restricting entity expansion or external resource access. An attacker can craft a malicious form file that, when opened by a developer in the IDE, causes the XML parser to access local files or process entities in a way that leaks information back to the attacker. The attack surface is confined to local file access on the affected system; there is no network propagation vector. The severity is constrained by the CVSS score of 3.3, which reflects the requirement for user interaction and the limited scope of potential damage.

Business impact

For organizations using IntelliJ IDEA, the risk is primarily to individual developers whose systems may be compromised or who may be socially engineered into opening malicious form files. The impact is low because the vulnerability does not enable system compromise, privilege escalation, or lateral movement. However, in environments where developers work with sensitive intellectual property or configuration data, accidental exposure of local files could result in information leakage. The practical risk depends on how closely developers are monitored and how well form file sources are controlled within your development workflow.

Affected systems

JetBrains IntelliJ IDEA versions prior to 2026.1 are affected. This includes all 2025.x versions and earlier releases. The vulnerability is specific to the UI Designer component; it does not affect command-line tools, build systems, or other IntelliJ platform-based IDEs unless they share the same UI Designer code. Organizations running IntelliJ IDEA Community Edition, Ultimate Edition, and educational licenses are all potentially vulnerable if they have not updated to version 2026.1 or later.

Exploitability

Exploitation is straightforward in concept but constrained by practical barriers. An attacker must either place a malicious form file (.form or related XML file) into a project repository that a developer will clone, or trick a developer into opening one directly. The CVSS vector AV:L (Attack Vector: Local) and UI:R (User Interaction: Required) confirm that the attacker has no remote path and must rely on social engineering or repository compromise. There is no known public exploit or weaponized proof-of-concept, and the vulnerability has not been added to the CISA Known Exploited Vulnerabilities catalog. This suggests real-world exploitation is unlikely to occur at scale, though the ease of crafting a malicious XML file means opportunistic attacks remain plausible if an attacker gains repository access.

Remediation

Upgrade IntelliJ IDEA to version 2026.1 or later to apply the fix to the UI Designer form parser. JetBrains has confirmed the vulnerability is resolved in 2026.1; verify the specific patch version in the official JetBrains security advisory. Users of older versions should prioritize this update if developers regularly work with form files from untrusted sources or if code repository integrity cannot be guaranteed. The upgrade is non-breaking for most workflows and should be tested in a development environment first.

Patch guidance

Download and install IntelliJ IDEA 2026.1 or later directly from the JetBrains website or through your IDE's built-in updater (Help > Check for Updates). Verify the update has been applied by navigating to Help > About and confirming the version number. Organizations using centralized license servers should coordinate the upgrade with their JetBrains administrator. There are no interim mitigations or configuration changes that reduce risk; update is the only remediation. Plan the rollout to avoid disrupting active development—consider phased deployment across teams if your organization runs a large fleet of IDEs.

Detection guidance

Monitor for suspicious form file modifications or additions to version control repositories. If a form file (.form or .xml in the UI Designer context) is committed by an unexpected user or contains external entity declarations, investigate further. Developers should report if they encounter unusual parsing warnings or errors when opening form files, as this may indicate a malicious payload. Enable IDE logging at the form parser level (if available in your IntelliJ configuration) to detect malicious entity expansion attempts. Standard endpoint detection and response (EDR) tools will not reliably detect this activity without form-file-specific rules; focus detection efforts on code review and version control auditing.

Why prioritize this

Although the CVSS score is low (3.3), this vulnerability warrants attention in your patch management queue because it affects a widely used development tool and requires only local user interaction. Prioritization should be moderate rather than urgent: patch it within your standard development tool update cycle (typically 2–4 weeks), but do not delay critical or high-severity patches to do so. The lack of KEV designation and public exploits reduces the priority compared to actively exploited vulnerabilities. However, development environments are often overlooked in patch management, so ensure this update is actually deployed rather than deferred indefinitely.

Risk score, explained

The CVSS 3.1 score of 3.3 reflects a low-severity vulnerability with limited attack surface and impact. The vector CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N indicates: local attack vector (no remote exploitation), low attack complexity (easy to craft malicious input once file is opened), no privilege requirement, mandatory user interaction, unchanged scope, low confidentiality impact (information disclosure only), no integrity or availability impact. The score does not include temporal or environmental factors; your organization's risk may be higher if developers frequently work with externally sourced form files or if your threat model includes insider threats with repository access.

Frequently asked questions