CVE-2021-33580Network attack vector

Unauthenticated service interruption via referrer regex

Published Aug 18, 2021 · Updated Aug 3, 2024

Regular expression denial of service in Apache Roller before 6.0.2 allows remote attackers to interrupt the server via a crafted Referer. Roller's referrer-processing logic builds and evaluates a regular expression from the Referer header, request URL, and query string, allowing catastrophic backtracking. No authentication or browser is required; one crafted HTTP request can consume server-side processing resources and interrupt service.

CVSS severity7.5
High
EPSS probability3.30%
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 Apache Roller before 6.0.2 allows remote attackers to interrupt the server via a crafted Referer. Roller's referrer-processing logic builds and evaluates a regular expression from the Referer header, request URL, and query string, allowing catastrophic backtracking. No authentication or browser is required; one crafted HTTP request can consume server-side processing resources and interrupt service.

The record

CVE
CVE-2021-33580
Published
Aug 18, 2021
Updated
Aug 3, 2024
Vendor
The Apache Software Foundation
Product
Apache Roller
Classifications
CWE-400, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 18, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record 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=Apache Roller <6.0.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Apache Software Foundation · Apache Rollerversion=Apache Roller <6.0.2

Published CVSS scores

4.3NISTAV:N/AC:M/Au:N/C:N/I:N/A:P
7.5NISTCVSS: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-400Uncontrolled Resource Consumption
T1499.004Application or System Exploitation

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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