Process crash via IO buffer overflow
Published Jun 30, 2026 · Updated Jun 30, 2026
Heap buffer overflow in Ruby JSON 2.9.0 through 2.19.8 allows remote attackers to crash applications via streamed JSON output. In ext/json/fbuffer/fbuffer.h, fbuffer_do_inc_capa() compares a requested write with total capacity rather than remaining capacity, so fbuffer_append_reserved() copies an attacker-controlled string past the IO buffer. Reachability requires an application to stream an attacker-controlled string near 16 KB through JSON.dump(obj, io) or JSON::State#generate(obj, io); the demonstrated consequence is process termination only.
Summary
What happened
Heap buffer overflow in Ruby JSON 2.9.0 through 2.19.8 allows remote attackers to crash applications via streamed JSON output. In ext/json/fbuffer/fbuffer.h, fbuffer_do_inc_capa() compares a requested write with total capacity rather than remaining capacity, so fbuffer_append_reserved() copies an attacker-controlled string past the IO buffer. Reachability requires an application to stream an attacker-controlled string near 16 KB through JSON.dump(obj, io) or JSON::State#generate(obj, io); the demonstrated consequence is process termination only.
The record
- CVE
- CVE-2026-54696
- Published
- Jun 30, 2026
- Updated
- Jun 30, 2026
- Vendor
- libwww-perl
- Product
- JSON
- Classifications
- CWE-787, CWE-131, CWE-122, T1499
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jun 30, 2026CVE publishedPublication date reported by the CVE source.
- Jun 30, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=>= 2.9.0, < 2.19.9
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Upstream JSON.dump IO-streaming proof of conceptproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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