CVE-2023-23621Network attack vector

Service interruption via unbounded user-agent regex

Published Jan 27, 2023 · Updated Mar 10, 2025

ReDoS in Discourse stable before 3.0.1 and beta 3.1.0.beta1 allows remote attackers to interrupt service via a crafted user agent. MobileDetection.modern_mobile_device? passed the entire User-Agent value to MODERN_MOBILE_REGEX, allowing crafted input to trigger excessive backtracking. An unauthenticated network request reaches the parser; the documented consequence is availability loss without data disclosure or modification.

CVSS severity8.6
High
EPSS probability0.87%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

ReDoS in Discourse stable before 3.0.1 and beta 3.1.0.beta1 allows remote attackers to interrupt service via a crafted user agent. MobileDetection.modern_mobile_device? passed the entire User-Agent value to MODERN_MOBILE_REGEX, allowing crafted input to trigger excessive backtracking. An unauthenticated network request reaches the parser; the documented consequence is availability loss without data disclosure or modification.

The record

CVE
CVE-2023-23621
Published
Jan 27, 2023
Updated
Mar 10, 2025
Vendor
Discourse
Product
Discourse
Classifications
CWE-1333, T1499.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 27, 2023CVE publishedPublication date reported by the CVE source.
  2. Mar 10, 2025Record 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=< 3.0.1
  2. Affected versionversion== 3.1.0.beta1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Discourse · Discourseversion=< 3.0.1; version== 3.1.0.beta1

Published CVSS scores

8.6GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
7.5NVDCVSS: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 exploitUnconfirmed

Weakness, pattern, technique

CWE-1333Inefficient Regular Expression Complexity
T1499.003Application Exhaustion Flood

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

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Your stack

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