CVE-2026-44288: protobufjs validation bypass via overlong UTF-8 sequences

CVE-2026-44288 · Severity: medium · CVSS 5.3 · Published 2026-05-13

A vulnerability in the protobufjs library, which is used to handle data serialization in JavaScript applications, could allow attackers to bypass security filters. By using specially crafted data sequences, an attacker can trick the system into accepting forbidden characters that were supposed to be blocked by initial security checks. This could lead to unauthorized data modification or the bypass of application-level security controls depending on how the decoded data is used.

Technologies: protobufjs (npm), Protobufjs Protobuf.Js. Vendors: npm, Protobufjs.

Quick answers

Is CVE-2026-44288 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-44288 being exploited in the wild.
How severe is CVE-2026-44288?
Medium severity, with a CVSS score of 5.3, published 13 May 2026.
Which products and versions are affected?
@protobufjs/utf8 (npm) SEMVER:introduced=0,fixed=1.1.1; protobufjs (npm) SEMVER:introduced=0,fixed=7.5.6; Protobufjs Protobuf.Js <= 7.5.5, >= 8.0.0 <= 8.0.1; Protobufjs Utf8 <= 1.1.0.
Is there a fix for CVE-2026-44288?
Yes. @protobufjs/utf8 (npm): upgrade to 1.1.1 or later; protobufjs (npm): upgrade to 7.5.6 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-44288 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-44288?
Check whether you run @protobufjs/utf8 (npm), protobufjs (npm), Protobufjs Protobuf.Js or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • @protobufjs/utf8 (npm): upgrade to 1.1.1 or later
    npm install @protobufjs/utf8@1.1.1
  • protobufjs (npm): upgrade to 7.5.6 or later
    npm install protobufjs@7.5.6

Technical details

The vulnerability exists in the minimal UTF-8 decoder used by protobufjs in non-Node.js environments or fallback paths. The decoder incorrectly accepts overlong UTF-8 sequences and decodes them to canonical characters instead of rejecting them or using replacement characters. An attacker can exploit this by providing malicious protobuf binary data that bypasses raw byte-level inspections (e.g., filters looking for specific ASCII characters) because the forbidden characters only appear after the non-strict decoding process. This is classified as Improper Handling of Unicode Encoding (CWE-176). The issue is resolved in versions 7.5.6 and 8.0.2.

Affected products

  • protobufjs protobufjs < 7.5.6, >= 8.0.0, < 8.0.2
  • protobufjs @protobufjs/utf8 <= 1.1.0

Identifiers

  • CVE-2026-44288
  • GHSA-q6x5-8v7m-xcrf

Timeline

  • 2026-05-12: advisory: GitHub Security Advisory published
  • 2026-05-13: disclosed: NVD publication date

References

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