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CVE-2026-4800

CRITICALCVSS 9.8/10EPSS 2.62%

Last modified

CVE-2026-4800 is a critical-severity vulnerability rated 9.8/10 on the CVSS scale. The fix for CVE-2021-23337 added validation for the variable option in _.template but did not apply the same validation to options.imports key names, and both paths flow into the same Function() constructor sink. When an application passes untrusted input as options.imports key names, an attacker can inject default-parameter expressions that execute arbitrary code at template compilation time. EPSS estimates a 2.62% chance of exploitation in the next 30 days.

Description

The fix for CVE-2021-23337 added validation for the variable option in _.template but did not apply the same validation to options.imports key names, and both paths flow into the same Function() constructor sink. When an application passes untrusted input as options.imports key names, an attacker can inject default-parameter expressions that execute arbitrary code at template compilation time. Additionally, _.template uses assignInWith to merge imports, which enumerates inherited properties via for..in, so if Object.prototype has been polluted by another vector the polluted keys are copied into the imports object and passed to Function(). The issue is fixed in 4.18.1 for lodash, lodash-es, lodash-amd, and lodash.template. As a workaround, do not pass untrusted input as key names in options.imports; use only developer-controlled, static key names.

Metrics

CVSS 3.1
9.8/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Probability
2.62%

85.2th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

VendorProductVersions
LodashLodash>= 4.0.0, < 4.18.0
LodashLodash-Amd>= 4.0.0, < 4.18.0
LodashLodash-Es>= 4.0.0, < 4.18.0
LodashLodash.Template>= 4.0.0, < 4.18.0

References

Timeline

Published
Last Modified
Status
Modified

Frequently Asked Questions

What is CVE-2026-4800?
The fix for CVE-2021-23337 added validation for the variable option in _.template but did not apply the same validation to options.imports key names, and both paths flow into the same Function() constructor sink. When an application passes untrusted input as options.imports key names, an attacker can inject default-parameter expressions that execute arbitrary code at template compilation time. Additionally, _.template uses assignInWith to merge imports, which enumerates inherited properties via for..in, so if Object.prototype has been polluted by another vector the polluted keys are copied into the imports object and passed to Function(). The issue is fixed in 4.18.1 for lodash, lodash-es, lodash-amd, and lodash.template. As a workaround, do not pass untrusted input as key names in options.imports; use only developer-controlled, static key names.
How severe is CVE-2026-4800?
CVE-2026-4800 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 2.62% probability of exploitation in the next 30 days.
How do I fix CVE-2026-4800?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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Source: NVD / NIST