CVE-2026-34483Network attack vector

JSON log injection via unescaped request targets

Published Apr 9, 2026 · Updated Apr 9, 2026

Improper output escaping in JsonAccessLogValve in Apache Tomcat allows remote attackers to inject arbitrary JSON into access logs via crafted URLs. AbstractAccessLogValve appends request URIs and query strings directly instead of calling escapeAndAppend, so relaxed characters preserve JSON syntax. Exposure requires JsonAccessLogValve plus non-default relaxedPathChars or relaxedQueryChars; unauthenticated requests can corrupt or forge structured log records.

CVSS severity7.5
High
EPSS probability0.46%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper output escaping in JsonAccessLogValve in Apache Tomcat allows remote attackers to inject arbitrary JSON into access logs via crafted URLs. AbstractAccessLogValve appends request URIs and query strings directly instead of calling escapeAndAppend, so relaxed characters preserve JSON syntax. Exposure requires JsonAccessLogValve plus non-default relaxedPathChars or relaxedQueryChars; unauthenticated requests can corrupt or forge structured log records.

The record

CVE
CVE-2026-34483
Published
Apr 9, 2026
Updated
Apr 9, 2026
Vendor
The Apache Software Foundation
Product
Apache Tomcat
Classifications
CWE-116, T1565.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 9, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 9, 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.

  1. Affected versionversion=10.1.0-M1 <=10.1.53
  2. Affected versionversion=11.0.0-M1 <=11.0.20
  3. Affected versionversion=8.5.84 <=8.5.100
  4. Affected versionversion=9.0.40 <=9.0.116

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Apache Software Foundation · Apache Tomcatversion=10.1.0-M1 <=10.1.53; version=11.0.0-M1 <=11.0.20; version=8.5.84 <=8.5.100; version=9.0.40 <=9.0.116

Published CVSS scores

7.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-116Improper Encoding or Escaping of Output
T1565.001Stored Data Manipulation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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