CVE-2023-27539Network attack vector

Service interruption via Accept-header regex backtracking

Published Jan 9, 2025 · Updated Jan 9, 2025

ReDoS in Rack 2.0.0 through 2.2.6.3 and 3.0.0 through 3.0.6 allows remote attackers to interrupt service via crafted headers. Rack::Request#parse_http_accept_header splits attacker-controlled Accept header fields with whitespace-matching regular expressions that can backtrack excessively. Unauthenticated requests to a Rack-backed application using this parser can monopolize processing time and interrupt service.

CVSS severity5.3
Medium
EPSS probability1.08%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

ReDoS in Rack 2.0.0 through 2.2.6.3 and 3.0.0 through 3.0.6 allows remote attackers to interrupt service via crafted headers. Rack::Request#parse_http_accept_header splits attacker-controlled Accept header fields with whitespace-matching regular expressions that can backtrack excessively. Unauthenticated requests to a Rack-backed application using this parser can monopolize processing time and interrupt service.

The record

CVE
CVE-2023-27539
Published
Jan 9, 2025
Updated
Jan 9, 2025
Vendor
Rack
Product
Rack
Classifications
T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 9, 2025CVE publishedPublication date reported by the CVE source.
  2. Jan 9, 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=2.2.6.4 <2.2.6.4
  2. Affected versionversion=3.0.6.1 <3.0.6.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Rack · Rackversion=2.2.6.4 <2.2.6.4; version=3.0.6.1 <3.0.6.1

Published CVSS scores

5.3CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
5.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

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

T1499Endpoint Denial of Service

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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