CVE-2026-33210Network attack vector

Data disclosure or application crash via format string

Published Mar 20, 2026 · Updated Mar 20, 2026

Format string injection in Ruby JSON allows remote attackers to disclose information or crash consuming applications via crafted JSON. The duplicate-key error path passes an attacker-controlled key as the format argument to rb_sprintf, causing percent directives to be interpreted instead of rendered literally. Exposure requires a consuming application to parse user-supplied documents with the nondefault allow_duplicate_key: false option.

CVSS severity8.3
High
EPSS probability0.86%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Format string injection in Ruby JSON allows remote attackers to disclose information or crash consuming applications via crafted JSON. The duplicate-key error path passes an attacker-controlled key as the format argument to rb_sprintf, causing percent directives to be interpreted instead of rendered literally. Exposure requires a consuming application to parse user-supplied documents with the nondefault allow_duplicate_key: false option.

The record

CVE
CVE-2026-33210
Published
Mar 20, 2026
Updated
Mar 20, 2026
Vendor
libwww-perl
Product
JSON
Classifications
CWE-134
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 20, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 20, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 2.14.0, < 2.15.2.1
  2. Affected versionversion=>= 2.16.0, < 2.17.1.2
  3. Affected versionversion=>= 2.18.0, < 2.19.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

libwww-perl · JSONversion=>= 2.14.0, < 2.15.2.1; version=>= 2.16.0, < 2.17.1.2; version=>= 2.18.0, < 2.19.2

Published CVSS scores

9.1NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
8.3GitHubCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:H/SC:N/SI:N/SA:N
9.1Red HatCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-134Use of Externally-Controlled Format String

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo