CVE-2026-12866: Code Execution in expr-eval
All versions of the package expr-eval are vulnerable to Code Execution via the toJSFunction() API. An attacker can execute arbitrary JavaScript by supplying crafted expressions that are compiled into native code using new Function(). Because user-controlled expressions are transformed directly into executable JavaScript, attackers can escape the intended expression sandbox and run arbitrary code within the application's context.
AI Analysis
Technical Summary
CVE-2026-12866 affects all versions of the expr-eval package. The vulnerability is due to the toJSFunction() API compiling user-supplied expressions into JavaScript code using new Function(), which allows attackers to execute arbitrary code by escaping the expression sandbox. This is a code injection vulnerability categorized under CWE-94 (Improper Control of Generation of Code). The CVSS 4.0 base score is 9.2, indicating a critical severity with network attack vector, low attack complexity, no privileges required, no user interaction, and high impact on confidentiality, integrity, and availability. No official patch or remediation guidance is currently available.
Potential Impact
Successful exploitation allows an unauthenticated attacker to execute arbitrary JavaScript code within the context of the vulnerable application. This can lead to full compromise of the application environment, including data theft, manipulation, or service disruption. The vulnerability affects confidentiality, integrity, and availability at a high level.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, avoid using the toJSFunction() API with untrusted input or implement strict input validation and sanitization to prevent malicious expressions from being processed.
CVE-2026-12866: Code Execution in expr-eval
Description
All versions of the package expr-eval are vulnerable to Code Execution via the toJSFunction() API. An attacker can execute arbitrary JavaScript by supplying crafted expressions that are compiled into native code using new Function(). Because user-controlled expressions are transformed directly into executable JavaScript, attackers can escape the intended expression sandbox and run arbitrary code within the application's context.
CVSS v4.0
Score 9.2critical
Affected software
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-12866 affects all versions of the expr-eval package. The vulnerability is due to the toJSFunction() API compiling user-supplied expressions into JavaScript code using new Function(), which allows attackers to execute arbitrary code by escaping the expression sandbox. This is a code injection vulnerability categorized under CWE-94 (Improper Control of Generation of Code). The CVSS 4.0 base score is 9.2, indicating a critical severity with network attack vector, low attack complexity, no privileges required, no user interaction, and high impact on confidentiality, integrity, and availability. No official patch or remediation guidance is currently available.
Potential Impact
Successful exploitation allows an unauthenticated attacker to execute arbitrary JavaScript code within the context of the vulnerable application. This can lead to full compromise of the application environment, including data theft, manipulation, or service disruption. The vulnerability affects confidentiality, integrity, and availability at a high level.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, avoid using the toJSFunction() API with untrusted input or implement strict input validation and sanitization to prevent malicious expressions from being processed.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- snyk
- Date Reserved
- 2026-06-22T08:22:34.991Z
- Cvss Version
- 4.0
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a3a187eeed863c81e3ed8ee
Added to database: 06/23/2026, 05:24:14 UTC
Last enriched: 07/08/2026, 10:46:49 UTC
Last updated: 08/05/2026, 00:41:11 UTC
Views: 226
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