4.8

CVE-2026-59876: protobufjs_project protobufjs Prototype Pollution

CVSS: 4.8v3.1MediumAnalyzed
AliasesGHSA-jfj6-75fj-8934CGA-22pp-vw5p-q4vhCGA-27jm-87j2-6gwj
Published 08-07-2026Last modified 09-07-2026
Open JSON

Vulnerability summary

CVE-2026-59876 is a medium (CVSS 4.8) Prototype Pollution vulnerability in protobufjs_project protobufjs. EPSS estimates a 0.35% chance of exploitation in the next 30 days, higher than 27% of scored vulnerabilities.

Overall risk
19/100
0100
Low · default modelHow is this calculated?
CVSS score
4.8/10
010
Medium · v3.1 (CVE.org)
EPSS score
0.35%
0%100%
Low · 0.00 pp in 30 days
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 0 · Related 1
CGA-V969-CF4M-H8W6

Timeline

  1. 08-07-2026
    PublishedVulnerability first disclosed.
  2. 09-07-2026
    Last modifiedVulnerability information updated.

Description

protobufjs compiles protobuf definitions into JavaScript (JS) functions. From 8.2.0 until 8.6.5, the protobufjs Text Format extension parsed string-keyed map entries using ordinary property assignment, allowing a map entry with key __proto__ to change the prototype of the returned map object instead of creating an own map entry in protobufjs/ext/textformat. This issue is fixed in version 8.6.5.

CVSS metrics

4 scores · 4 sources · 1 version

EPSS trend

Probability

0.35%

Chance of exploitation in the next 30 days

Percentile

27%

Versus all other CVEs

30-day change

0.00 pp

From 0.35% on 19-09-2026

19-09-202619-10-2026
EPSS score
0.35%

Known exploited

Compare KEV catalogs

Not in any of the 3 tracked catalogs.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Chainguard1 product
  • librechat< 0.8.7-r5
Npm1 product
  • protobufjs≥ 8.2.0, < 8.6.5
Protobufjs1 product
Protobufjs_project1 product

4 vendors · 4 products

References

7 links