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GHSA-r5fr-rjxr-66jc CVE-2026-4800

lodash vulnerable to Code Injection via `_.template` imports key names

Critical npm
Severity
8.1 / 10
Critical · CVSS 3.1
Exploit chance (EPSS)
2.81%
Chance of exploitation in the next 30 days. Higher than 86.51% of scored vulnerabilities.
Known exploited
No
Not in CISA's catalog
Weakness
CWE-94 Improper Control of Generation of Code ('Code Injection')
Fix
Available
4 packages have a fixed version

Description

Impact

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. 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. If Object.prototype has been polluted by any other vector, the polluted keys are copied into the imports object and passed to Function().

Patches

Users should upgrade to version 4.18.0.

The fix applies two changes:

  1. Validate importsKeys against the existing reForbiddenIdentifierChars regex (same check already used for the variable option)
  2. Replace assignInWith with assignWith when merging imports, so only own properties are enumerated

Workarounds

Do not pass untrusted input as key names in options.imports. Only use developer-controlled, static key names.

Affected versions

npm

PackageVulnerableFixed in
lodash
>= 4.0.0, <= 4.17.23
 No fix yet
lodash
>= 4.0.0, < 4.18.0
4.18.0
lodash-amd
>= 4.0.0, <= 4.17.23
 No fix yet
lodash-amd
>= 4.0.0, < 4.18.0
4.18.0
lodash-es
>= 4.0.0, <= 4.17.23
 No fix yet
lodash-es
>= 4.0.0, < 4.18.0
4.18.0
lodash.template
>= 4.0.0, < 4.18.0
4.18.0
lodash.template
>= 4.0.0, < 4.18.0
4.18.0

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

lodash npm → 4.18.0

npm
npm install lodash@4.18.0
yarn
yarn add lodash@4.18.0
pnpm
pnpm add lodash@4.18.0

lodash-amd npm → 4.18.0

npm
npm install lodash-amd@4.18.0
yarn
yarn add lodash-amd@4.18.0
pnpm
pnpm add lodash-amd@4.18.0

lodash-es npm → 4.18.0

npm
npm install lodash-es@4.18.0
yarn
yarn add lodash-es@4.18.0
pnpm
pnpm add lodash-es@4.18.0

lodash.template npm → 4.18.0

npm
npm install lodash.template@4.18.0
yarn
yarn add lodash.template@4.18.0
pnpm
pnpm add lodash.template@4.18.0

Severity breakdown

CVSS 3.1 8.1

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

Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

Weakness

CWE-94: Improper Control of Generation of Code ('Code Injection')

The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment.

How to prevent it
  • Architecture and Design: Refactor your program so that you do not have to dynamically generate code.
  • Architecture and Design: Run your code in a "jail" or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict which code can be executed by your product. Examples include the Unix chroot jail and AppArmor. In general, managed code may provide some protection. This may not be a feasible solution, and it only limits the impact to the operating system; the rest of your application may still be subject to compromise. Be careful to avoid CWE-243 and other weaknesses related to jails.
  • Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright. To reduce the likelihood of code injection, use stringent allowlists that limit which constructs are allowed. If you are dynamically constructing code that invokes a function, then verifying that the input is alphanumeric might be insufficient. An attacker might still be able to reference a dangerous function that you did not intend to allow, such as system(), exec(), or exit().
  • Testing: Use dynamic tools and techniques that interact with the product using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. The product's operation may slow down, but it should not become unstable, crash, or generate incorrect results.
  • Operation: Run the code in an environment that performs automatic taint propagation and prevents any command execution that uses tainted variables, such as Perl's "-T" switch. This will force the program to perform validation steps that remove the taint, although you must be careful to correctly validate your inputs so that you do not accidentally mark dangerous inputs as untainted (see CWE-183 and CWE-184).
  • Operation: Run the code in an environment that performs automatic taint propagation and prevents any command execution that uses tainted variables, such as Perl's "-T" switch. This will force the program to perform validation steps that remove the taint, although you must be careful to correctly validate your inputs so that you do not accidentally mark dangerous inputs as untainted (see CWE-183 and CWE-184).
  • Implementation: For Python programs, it is frequently encouraged to use the ast.literal_eval() function instead of eval, since it is intentionally designed to avoid executing code. However, an adversary could still cause excessive memory or stack consumption via deeply nested structures [REF-1372], so the python documentation discourages use of ast.literal_eval() on untrusted data [REF-1373].

References

Advisories

Fixes and patches

Packages

Other links

Timeline

  1. Published
  2. Last updated by the source
  3. Latest EPSS score
AdvisorySeverityWhy it's related
GHSA-f23m-r3pf-42rh
lodash vulnerable to Prototype Pollution via array path bypass in `_.unset` and `_.omit`
Medium Also affects lodash
GHSA-xxjr-mmjv-4gpg
Lodash has Prototype Pollution Vulnerability in `_.unset` and `_.omit` functions
Medium Also affects lodash
GHSA-29mw-wpgm-hmr9
Regular Expression Denial of Service (ReDoS) in lodash
Medium Also affects lodash
GHSA-35jh-r3h4-6jhm
Command Injection in lodash
High Also affects lodash
GHSA-p6mc-m468-83gw
Prototype Pollution in lodash
High Also affects lodash
GHSA-x5rq-j2xg-h7qm
Regular Expression Denial of Service (ReDoS) in lodash
Medium Also affects lodash
GHSA-jf85-cpcp-j695
Prototype Pollution in lodash
Critical Also affects lodash
GHSA-4xc9-xhrj-v574
Prototype Pollution in lodash
High Also affects lodash

Credits: M0nd0R, UlisesGascon, bugbunny-research, dolevmiz1, falsyvalues, jdalton, jonchurch, threalwinky

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