GHSA-66ff-xgx4-vchm CVE-2026-44293

protobuf.js: Code injection through bytes field defaults in generated toObject code

High npm

Severity: 0.0 / 10; High · CVSS 4.0
Exploit chance (EPSS): 0.41%; Chance of exploitation in the next 30 days. Higher than 35.02% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-94 Improper Control of Generation of Code ('Code Injection')
Fix: 7.5.6; Upgrade protobufjs to this version or later

Description

Summary

protobufjs generated JavaScript for toObject conversion could include an unsafe expression derived from a schema-controlled bytes field default value. A crafted descriptor with a non-string default value for a bytes field could cause attacker-controlled code to be emitted into the generated conversion function.

Impact

An attacker who can provide or influence a protobuf descriptor may be able to execute arbitrary JavaScript in the context of the process using protobufjs.

This requires the application to load an attacker-controlled schema or descriptor and then convert a message of the affected type with defaults enabled. Applications that only use trusted, application-defined schemas are not directly affected by this issue.

Preconditions

The application must allow an attacker to control or influence a protobuf JSON descriptor or equivalent reflected schema.
The descriptor must define a bytes field with an attacker-controlled default value.
The application must call toObject with defaults enabled for the affected type.

Workarounds

Do not load protobuf schemas or JSON descriptors from untrusted sources with affected versions. If untrusted schemas must be accepted, validate or restrict field options before loading them and run schema processing in an isolated environment.

Affected versions

npm

Package	Vulnerable	Fixed in
protobufjs	`< 7.5.6`	`7.5.6`
protobufjs	`>= 8.0.0, < 8.0.2`	`8.0.2`

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.

protobufjs npm → `7.5.6`

npm

npm install protobufjs@7.5.6

yarn

yarn add protobufjs@7.5.6

pnpm

pnpm add protobufjs@7.5.6

Severity breakdown

CVSS 4.0 0.0

CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Attack vector: Network
Attack complexity: Low
Attack requirements: Present
Privileges required: Low
User interaction: None
Confidentiality (vulnerable system): High
Integrity (vulnerable system): High
Availability (vulnerable system): High
Confidentiality (subsequent systems): None
Integrity (subsequent systems): None
Availability (subsequent systems): None

CVSS 3.1 8.8

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

Attack vector: Network
Attack complexity: Low
Privileges required: Low
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

Packages

github.com/protobufjs/protobuf.js

Timeline

May 12, 2026 Published
Sep 10, 2026 Last updated by the source
Nov 1, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-j3f2-48v5-ccww protobufjs: Denial of Service via infinite loop in .proto option parsing	High	Also affects protobufjs
GHSA-jfj6-75fj-8934 protobufjs: Text Format string map parsing can mutate returned map object prototype	Medium	Also affects protobufjs
GHSA-94rc-8x27-4472 protobufjs: Memory amplification from preserved unknown fields in binary decode	Medium	Also affects protobufjs
GHSA-wcpc-wj8m-hjx6 protobufjs: Denial of service through unbounded Any expansion during JSON conversion	High	Also affects protobufjs
GHSA-f38q-mgvj-vph7 protobufjs : Schema-derived names can shadow runtime-significant properties	Medium	Also affects protobufjs
GHSA-jggg-4jg4-v7c6 protobufjs: Denial of Service via unbounded recursive JSON descriptor expansion	High	Also affects protobufjs
GHSA-2pr8-phx7-x9h3 protobuf.js: Denial of service from crafted field names in generated code	Medium	Also affects protobufjs
GHSA-fx83-v9x8-x52w protobuf.js: Prototype injection in generated message constructors	Medium	Also affects protobufjs

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