CVE-2026-34939Public exploitNetwork attack vector

Service hang via catastrophic regex backtracking

Published Apr 3, 2026 · Updated Apr 3, 2026

Regular expression denial of service in PraisonAI before 4.5.90 allows remote attackers to hang the MCP server via a crafted query. MCPToolIndex.search_tools() passes its caller-controlled query directly to re.compile() and searches tool names and hints without validation or a timeout. The HTTP transport accepts requests without an API key by default, and one query blocks the Python thread for hundreds of seconds.

CVSS severity6.5
Medium
EPSS probability0.40%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Regular expression denial of service in PraisonAI before 4.5.90 allows remote attackers to hang the MCP server via a crafted query. MCPToolIndex.search_tools() passes its caller-controlled query directly to re.compile() and searches tool names and hints without validation or a timeout. The HTTP transport accepts requests without an API key by default, and one query blocks the Python thread for hundreds of seconds.

The record

CVE
CVE-2026-34939
Published
Apr 3, 2026
Updated
Apr 3, 2026
Vendor
Mervin Praison
Product
PraisonAI
Classifications
CWE-1333, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 3, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 3, 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=< 4.5.90

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mervin Praison · PraisonAIversion=< 4.5.90

Published CVSS scores

6.5GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/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 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 exploitPublished

Weakness, pattern, technique

CWE-1333Inefficient Regular Expression Complexity
T1499.004Application or System Exploitation

Public exploit references

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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