CVE-2021-4306Network attack vector

Application stall via markupWidth regular-expression backtracking

Published Jan 7, 2023 · Updated Aug 3, 2024

Regular expression denial of service in Cronvel Terminal Kit 2.1.0 through 2.1.7 allows attackers to stall applications via crafted markup. misc.markupWidth applies an ambiguous, backtracking regular expression to markup text; repeated '^[' prefixes force excessive matching work. An application must pass attacker-controlled markup to this library routine; processing can monopolize CPU and stall the hosting process.

CVSS severity7.5
High
EPSS probability0.95%
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 Cronvel Terminal Kit 2.1.0 through 2.1.7 allows attackers to stall applications via crafted markup. misc.markupWidth applies an ambiguous, backtracking regular expression to markup text; repeated '^[' prefixes force excessive matching work. An application must pass attacker-controlled markup to this library routine; processing can monopolize CPU and stall the hosting process.

The record

CVE
CVE-2021-4306
Published
Jan 7, 2023
Updated
Aug 3, 2024
Vendor
Cronvel
Product
Terminal Kit
Classifications
CWE-1333, CAPEC-492, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 7, 2023CVE 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=2.1.0
  2. Affected versionversion=2.1.1
  3. Affected versionversion=2.1.2
  4. Affected versionversion=2.1.3
  5. Affected versionversion=2.1.4
  6. Affected versionversion=2.1.5
  7. Affected versionversion=2.1.6
  8. Affected versionversion=2.1.7

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Cronvel · Terminal Kitversion=2.1.0; version=2.1.1; version=2.1.2; version=2.1.3; version=2.1.4; version=2.1.5; version=2.1.6; version=2.1.7

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
3.5VulDBCVSS:3.1/AV:A/AC:L/PR:L/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 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
CAPEC-492Regular Expression Exponential Blowup
T1499.004Application or System Exploitation

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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