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Fencer Intel
medium 4.8

CVE-2026-59876 json

protobufjs: Text Format string map parsing can mutate returned map object prototype

published 4mo ago modified 17d ago also EUVD-2026-42311 , GHSA-jfj6-75fj-8934

cvss
4.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 28%
public exploits
0
none known

Summary

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.

Patch / fix

  • npm protobufjs 8.6.5
  • protobufjs_project protobufjs 8.6.5

Is CVE-2026-59876 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-59876 updated cvss 4.8

protobufjs: protobufjs: Prototype pollution vulnerability in Text Format extension

  • Red Hat Ceph Storage 9 rhceph/alloy-rhel10
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Cryostat 4 grafana-infinity-datasource-npm Red Hat OpenShift Pipelines openshift-pipelines/pipelines-console-plugin-rhel8, openshift-pipelines/pipelines-console-plugin-rhel9, openshift-pipelines/pipelines-console-plugin-pf5-rhel9 Red Hat OpenShift Service Mesh 3 openshift-service-mesh/kiali-rhel9, openshift-service-mesh/kiali-ossmc-rhel9 Red Hat Ansible Automation Platform 2 automation-platform-ui 2.6.10-1.el9ap, ansible-automation-platform-26/gateway-rhel9, ansible-automation-platform-27/gateway-rhel9 Red Hat Build of Podman Desktop rh-podman-desktop.git Red Hat Developer Hub 1 rhdh/rhdh-hub-rhel9
    +2 more products
    Red Hat Enterprise Linux 8 grafana, grafana-loki, grafana-mssql, grafana-mysql, grafana-selinux, grafana-graphite, +8 more Red Hat Enterprise Linux AI (RHEL AI) 3 rhelai3/bootc-cuda-rhel9, rhelai3/bootc-rocm-rhel9, rhelai3/bootc-gaudi-rhel9, rhelai3/disk-image-cuda-rhel9
    not affected: vulnerable code not present
  • Red Hat Hardened Images dotnet9.0 9.0.118-1.hum1
    not affected: component not present
  • Red Hat OpenShift Container Platform 4 openshift4/ose-console, openshift4/ose-console-rhel9 Red Hat OpenShift Container Platform 5 openshift5/ose-console-rhel9 Red Hat Openshift Data Foundation 4 odf4/mcg-core-rhel9 Red Hat Self-service automation portal 2 ansible-automation-platform/automation-portal, ansible-automation-platform/bootc-automation-portal-rhel9
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
4mo ago

Exploit prediction

0.35% chance of exploitation in the next 30 days, higher than 28% of all scored CVEs (FIRST EPSS, 2026-11-11).

CVSS scores

assigned by version score vector
CNA 3.1 4.8 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
GitHub 3.1 4.8 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
NVD 3.1 4.8 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

Affected packages

ecosystem package affected fixed in
npm protobufjs
>=8.2.0, <8.6.5
8.6.5

Affected products

  • protobufjs protobuf.js

Classification

Weakness
  • CWE-1321 Improperly Controlled Modification of Object Prototype Attributes

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

The maintainers of protobufjs/protobuf.js published their own advisory on GitHub. Reviewed sources take precedence over it.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.