CVE-2026-100265: 
NixOS vulnerability analysis and mitigation

CVE-2026-100265 is a vulnerability in JetBrains Rider's AI Assistant component that allows third-party skills to be auto-updated without user confirmation. All versions of JetBrains Rider before 2026.2.1 are affected. The vulnerability was published on September 30, 2026, and is classified as CWE-494 (Download of Code Without Integrity Check). It carries a CVSS v3.1 base score of 4.8 (Medium), though Feedly's category estimate flags it as HIGH severity (JetBrains).

The root cause is classified as CWE-494 (Download of Code Without Integrity Check), meaning the AI Assistant feature in JetBrains Rider can silently download and apply updates to third-party skills without verifying their integrity or obtaining explicit user consent. The attack vector is network-based with high attack complexity and requires no privileges or user interaction, suggesting an adversary-in-the-middle or supply chain scenario where a malicious update could be injected. This maps to CAPEC patterns including Malicious Software Update (CAPEC-186), Malicious Automated Software Update via Redirection (CAPEC-187), and Malicious Automated Software Update via Spoofing (CAPEC-657) (JetBrains).

Successful exploitation could result in limited confidentiality and integrity impacts — an attacker who can intercept or spoof the update channel for AI Assistant third-party skills could cause Rider to silently install malicious skill code on a developer's workstation. This could expose sensitive project data or source code accessible within the IDE environment, or introduce malicious behavior into the development workflow. Availability is not impacted, and the scope is unchanged, limiting the blast radius to the affected Rider instance (JetBrains).

As of the publication date, there are no known public proof-of-concept exploits, no reported in-the-wild exploitation, and the CVE is not listed in the CISA Known Exploited Vulnerabilities catalog. The EPSS score is 0.0, reflecting a very low probability of exploitation in the near term. The NVD SSVC assessment confirms exploitation status as "none" and notes the vulnerability is not automatable (JetBrains).

1. Reconnaissance: Identify targets using JetBrains Rider with the AI Assistant feature enabled and third-party skills configured, running versions prior to 2026.2.1.
2. Position for interception: Establish a network-level adversary-in-the-middle position between the target developer workstation and JetBrains' skill update infrastructure (e.g., via ARP spoofing, DNS poisoning, or a rogue Wi-Fi access point).
3. Intercept update request: Capture the outbound HTTP/HTTPS request from Rider's AI Assistant when it checks for or downloads third-party skill updates.
4. Inject malicious skill payload: Serve a crafted, malicious skill package in response to the update request. Because no integrity check is performed, Rider will accept and install the tampered package without prompting the user.
5. Achieve code execution within IDE context: The malicious skill executes within the Rider AI Assistant environment, potentially accessing project files, credentials stored in the IDE, or performing other actions within the developer's workspace (JetBrains).

• Network: Unexpected outbound connections from the Rider process to unfamiliar or non-JetBrains domains during AI Assistant skill update operations; anomalous DNS resolutions for JetBrains update endpoints.
• File System: Newly created or modified AI Assistant skill files in the Rider plugins/skills directory that do not correspond to user-initiated installations; unexpected files with unusual timestamps in the JetBrains Rider application data folder.
• Logs: Rider or IDE logs showing skill update events that were not triggered by the user; error messages related to skill loading from unexpected sources.
• Process: Unusual child processes or network activity spawned by the JetBrains Rider process following an AI Assistant skill update event.

JetBrains has released JetBrains Rider 2026.2.1, which addresses this vulnerability by requiring user confirmation before auto-updating third-party AI Assistant skills. Users should upgrade to version 2026.2.1 or later as the primary remediation. As a temporary workaround, users can disable the AI Assistant feature or avoid configuring third-party skills until the patch is applied. Organizations should also ensure developer workstations use trusted network paths and consider monitoring for unexpected skill update activity (JetBrains).