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Fencer Vulns
medium 5.9

CVE-2026-27601 json

Underscore.js has unlimited recursion in _.flatten and _.isEqual, potential for DoS attack

published 2026-03-03 8 mo ago modified 2026-09-10 1 mo ago also EUVD-2026-9341 , GHSA-qpx9-hpmf-5gmw

cvss
5.9
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.1%
EPSS 1.1% chance of exploitation in 30 days, percentile 64%
public exploits
0
none known

Summary

Underscore.js is a utility-belt library for JavaScript. Prior to 1.13.8, the _.flatten and _.isEqual functions use recursion without a depth limit. Under very specific conditions, detailed below, an attacker could exploit this in a Denial of Service (DoS) attack by triggering a stack overflow. Untrusted input must be used to create a recursive datastructure, for example using JSON.parse, with no enforced depth limit. The datastructure thus created must be passed to _.flatten or _.isEqual. In the case of _.flatten, the vulnerability can only be exploited if it is possible for a remote client to prepare a datastructure that consists of arrays at all levels AND if no finite depth limit is passed as the second argument to _.flatten. In the case of _.isEqual, the vulnerability can only be exploited if there exists a code path in which two distinct datastructures that were submitted by the same remote client are compared using _.isEqual. For example, if a client submits data that are stored in a database, and the same client can later submit another datastructure that is then compared to the data that were saved in the database previously, OR if a client submits a single request, but its data are parsed twice, creating two non-identical but equivalent datastructures that are then compared. Exceptions originating from the call to _.flatten or _.isEqual, as a result of a stack overflow, are not being caught. This vulnerability is fixed in 1.13.8.

Patch / fix

  • npm underscore 1.13.8
  • underscorejs underscore 1.13.8
  • underscore Debian 14 1.13.8~dfsg+~1.13.0-1

debian advisories DEBIAN-CVE-2026-27601

  • velociraptor openSUSE Tumbleweed 0.76.7.0.git145.b60ef1146-1.1
  • agama-web-ui openSUSE Leap 16.0 17+673.b97ba64d6-160000.12.1
  • python-nbclassic openSUSE Tumbleweed 1.3.3-1.1
  • python-bqplot openSUSE Tumbleweed 0.12.45-14.1
  • python-ipympl openSUSE Tumbleweed 0.9.7-17.1

opensuse advisories openSUSE-SU-2026:12070-1openSUSE-SU-2026:21448-1openSUSE-SU-2026:10440-1openSUSE-SU-2026:10424-1openSUSE-SU-2026:10427-1

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-2026-27601 updated cvss 5.9

Underscore.js: Underscore.js: Denial of Service via recursive data structures in flatten and isEqual functions

  • Red Hat Logging Subsystem for Red Hat OpenShift openshift-logging/kibana6-rhel8, openshift-logging/elasticsearch6-rhel9, openshift-logging/logging-curator5-rhel9, openshift-logging/elasticsearch-proxy-rhel9, openshift-logging/elasticsearch-rhel9-operator, openshift-logging/elasticsearch-operator-bundle Red Hat Migration Toolkit for Virtualization mtv-candidate/mtv-console-plugin-rhel9, migration-toolkit-virtualization/mtv-console-plugin-rhel9 Red Hat OpenShift Pipelines openshift-pipelines/pipelines-hub-ui-rhel8, openshift-pipelines/pipelines-hub-api-rhel8, openshift-pipelines/pipelines-hub-db-migration-rhel8 Red Hat Advanced Cluster Management for Kubernetes 2 rhacm2/console-rhel9 Red Hat Ansible Automation Platform 2 ansible-automation-platform-24/lightspeed-rhel8, ansible-automation-platform-25/lightspeed-rhel8, ansible-automation-platform-26/lightspeed-rhel9, ansible-on-clouds/aoc-azure-aap-installer-rhel9 Red Hat Enterprise Linux 7 firefox
    +1 more products
    Red Hat Enterprise Linux 8 firefox, grafana, mozjs60, thunderbird, grafana-loki, grafana-mssql, +11 more
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Enterprise Linux 9 gjs, firefox, grafana, dotnet7.0, dotnet-host, firefox-x11, +14 more
    affected: workaround, no fix available, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 10 gjs, firefox, thunderbird Red Hat Enterprise Linux AI (RHEL AI) 3 rhelai3/bootc-cuda-rhel9, rhelai3/disk-image-cuda-rhel9 Red Hat Fuse 7 io.hawt-project, io.hawt-hawtio-online Red Hat JBoss Enterprise Application Platform 7 io.hawt-project Red Hat JBoss Enterprise Application Platform 8 io.hawt-project Red Hat JBoss Enterprise Application Platform Expansion Pack io.hawt-project
    +5 more products
    Red Hat OpenShift AI (RHOAI) rhoai/odh-dashboard-rhel8, rhoai/odh-dashboard-rhel9, rhoai/odh-mod-arch-gen-ai-rhel9, rhoai/odh-notebook-controller-rhel8, rhoai/odh-kf-notebook-controller-rhel8, rhoai/odh-mod-arch-model-registry-rhel9 Red Hat OpenShift Dev Spaces devspaces/code-rhel9, devspaces/openvsx-rhel9, devspaces/pluginregistry-rhel9 Red Hat Quay 3 quay/quay-rhel8, quay/quay-rhel9 Red Hat Satellite 6 satellite/iop-host-inventory-frontend-rhel9 Red Hat Self-service automation portal 2 ansible-automation-platform/automation-portal
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Developer Hub 1.8 rhdh 1776784286
    fixed: vendor fix RHSA-2026:9742
  • Red Hat Developer Hub 1.9 rhdh 1777903262
    fixed: vendor fix RHSA-2026:13826
  • Red Hat Developer Hub 1.10 rhdh/rhdh-hub-rhel9 1780930740
    fixed: vendor fix RHSA-2026:24841
  • Red Hat Developer Hub 1.8 rhdh 1776783947, rhdh 1776787729 Red Hat Developer Hub 1.9 rhdh 1777902709, rhdh 1777909942 Red Hat Developer Hub 1.10 rhdh/rhdh-rhel9-operator 1779927546, rhdh/rhdh-operator-bundle 1780961472
    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
8 mo ago

Exploit prediction

1.06% chance of exploitation in the next 30 days, higher than 64% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/jashkenas/underscore/security/advisories/GHSA-qpx9-hpmf-5gmw referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 4.0 8.2 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
GitHub 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
CNA 4.0 8.2 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
NVD 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
npm underscore
<1.13.8
1.13.8

Affected products

  • jashkenas underscore

Classification

Weakness
  • CWE-770 Allocation of Resources Without Limits or Throttling
  • CWE-674 Uncontrolled Recursion

References

Sources

Fencer Vulns 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.

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