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Fencer Intel
high 8.7

CVE-2026-71847 json

Ruby JSON: JSON::ResumableParser#partial_value dereferences a freed input buffer and crashes on truncated duplicate-key streams

published 3mo ago modified 18d ago also EUVD-2026-54576 , GHSA-9hj4-r449-hfvc

cvss
8.7
version 4.0, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 37%
public exploits
0
none known

Summary

Ruby JSON is a JSON implementation for Ruby. From 2.20.0 until 2.21.2, Ruby's JSON native C extension clears the consumed JSON::ResumableParser input buffer but leaves state.start, state.cursor, and state.end pointing into released storage. When partial_value reconstructs an incomplete object containing duplicate keys, the duplicate-key warning path calls cursor_position, which dereferences those stale pointers. This results in a heap-use-after-free and can terminate the Ruby process. An attacker who can supply JSON stream data to an application using JSON::ResumableParser may cause process termination when the application calls partial_value on incomplete attacker-controlled input containing duplicate object keys. This issue has been fixed in version 2.21.2.

Patch / fix

  • rubygems json 2.21.2
  • ruby-lang javascript_object_notation 2.21.2
  • ruby-lang json 2.21.2
  • rubygems json_gem 2.21.2
  • ruby-json Debian 14 2.21.2+dfsg-1

debian advisories DEBIAN-CVE-2026-71847

  • hawk2 SLE High Availability Extension 16.0, SLES for SAP applications 16.0 2.7.2+git.1788518533.7d4dadd6-160000.1.1

suse advisories SUSE-SU-2026:24195-1SUSE-SU-2026:24250-1

  • hawk2 openSUSE Tumbleweed 2.7.2+git.1792148770.648dcddb-1.1
  • hawk2 openSUSE Leap 16.0 2.7.2+git.1788518533.7d4dadd6-160000.1.1

opensuse advisories openSUSE-SU-2026:12153-1openSUSE-SU-2026:22068-1

Is CVE-2026-71847 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-2026-71847 updated cvss 5.9

json: Ruby JSON: Denial of Service via heap-use-after-free in JSON::ResumableParser

  • Red Hat 3scale API Management Platform 2 3scale-amp2/zync-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
Proof of concept is public
Automatable
yes
Technical impact
partial
Assessed
3mo ago

Exploit prediction

0.43% chance of exploitation in the next 30 days, higher than 37% of all scored CVEs (FIRST EPSS, 2026-11-11).

Exploits and checks

  • github.com https://github.com/ruby/json/security/advisories/GHSA-9hj4-r449-hfvc referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 4.0 8.7 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
CNA 4.0 8.7 CVSS:4.0/AV:N/AC:L/AT:N/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

Affected packages

ecosystem package affected fixed in
rubygems json
>=2.20.0, <2.21.2
2.21.2

Affected products

  • ruby json

Classification

Weakness

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.

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