CVE-2026-12957 Overview
CVE-2026-12957 is an improper trust boundary enforcement vulnerability in AWS Language Servers before version 1.65.0. The flaw allows arbitrary code execution when a local user opens a maliciously crafted workspace and trusts it when prompted. Commands defined in project configuration files execute automatically once workspace trust is granted. The vulnerability is tracked under CWE-732: Incorrect Permission Assignment for Critical Resource and affects all supported platforms running vulnerable Language Server versions.
Critical Impact
Local attackers can achieve arbitrary code execution in the context of the developer by distributing a malicious workspace that the user opens and trusts.
Affected Products
- AWS Language Servers prior to version 1.65.0
- All supported platforms running AWS Language Servers
- Development environments and IDE extensions consuming the AWS Language Server protocol
Discovery Timeline
- 2026-06-23 - CVE-2026-12957 published to NVD
- 2026-06-23 - Last updated in NVD database
Technical Details for CVE-2026-12957
Vulnerability Analysis
The vulnerability stems from improper enforcement of trust boundaries between user-controlled workspace content and the privileged Language Server runtime. Language Servers process project configuration files to provide code intelligence features such as completion, linting, and diagnostics. In affected versions, configuration directives within these files can specify commands that the Language Server executes automatically once the user trusts the workspace.
Attackers exploit this trust model by crafting workspaces containing malicious configuration. When a developer opens the workspace and approves the trust prompt, embedded commands run with the privileges of the local user. The attack does not require network access or elevated privileges, but it does require user interaction to grant workspace trust.
The issue maps to CWE-732, reflecting overly permissive handling of configuration data that should remain isolated from execution contexts. The EPSS score is 0.118% indicating low predicted exploitation activity, but the local code execution impact remains high.
Root Cause
The root cause is the absence of a strict trust boundary between declarative project configuration and command execution. Configuration files that should be parsed as data are instead interpreted in a way that triggers process invocation. The workspace trust prompt provides limited mitigation because users frequently approve trust for repositories without auditing every configuration file.
Attack Vector
The attack vector is local with required user interaction. An attacker prepares a repository or archive containing a poisoned project configuration. The victim clones, downloads, or opens the workspace in an IDE backed by the AWS Language Server. Once the victim accepts the workspace trust prompt, the Language Server reads the configuration and executes the attacker-defined commands. Refer to the AWS Security Bulletin 2026-047 and the GitHub Security Advisory GHSA-xhcr-j4j9-3gh7 for vendor-confirmed technical details.
Detection Methods for CVE-2026-12957
Indicators of Compromise
- Unexpected child processes spawned by IDE or Language Server host processes shortly after a workspace is opened
- Outbound network connections from developer machines initiated by shells or scripting interpreters launched by the IDE
- Recently cloned repositories containing project configuration files with embedded command directives or shell invocations
- New persistence artifacts created in user profile directories immediately following workspace trust acceptance
Detection Strategies
- Monitor process lineage for command interpreters such as bash, sh, powershell.exe, or cmd.exe whose parent process is an IDE or Language Server binary
- Alert on file write events to project configuration files in cloned repositories paired with subsequent process execution
- Inspect Language Server logs for command execution entries originating from workspace configuration parsing
- Correlate workspace trust acceptance events with process creation telemetry within a narrow time window
Monitoring Recommendations
- Collect endpoint process creation telemetry from developer workstations and forward to a centralized analytics platform
- Track installed versions of AWS Language Servers across the developer fleet to identify unpatched hosts
- Audit code review and repository ingestion workflows for unsigned or untrusted project configuration changes
- Establish a baseline for normal Language Server child process activity to surface anomalous executions
How to Mitigate CVE-2026-12957
Immediate Actions Required
- Upgrade AWS Language Servers to version 1.65.0 or later on every developer workstation and build agent
- Identify and remove any cloned repositories of unknown provenance opened during the exposure window
- Instruct developers to decline workspace trust prompts for any repository whose source is not verified
- Review recent process execution logs on developer endpoints for signs of exploitation
Patch Information
AWS resolved the issue in Language Servers version 1.65.0. Users must upgrade to this release or later to remediate CVE-2026-12957. Patch details are documented in the AWS Security Bulletin 2026-047 and the GitHub Security Advisory GHSA-xhcr-j4j9-3gh7.
Workarounds
- Disable or uninstall the AWS Language Server extension until the upgrade to 1.65.0 is completed
- Open untrusted repositories only inside isolated virtual machines or disposable containers
- Inspect project configuration files manually before granting workspace trust in the IDE
- Restrict developer accounts to least privilege so that any executed command runs with minimal permissions
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
