CVE-2021-39229Public exploitNetwork attack vector

Service hang via inefficient IFTTT URL regex

Published Sep 20, 2021 · Updated Aug 4, 2024

Regular expression denial of service in Apprise before 0.9.5.1 allows remote attackers to hang a hosting process via a crafted IFTTT URL. NotifyIFTTT.parse_native_url applies nested, overlapping repetition to attacker-controlled event-path characters, causing excessive backtracking. The path is reachable when a publicly hosted application grants access to the bundled IFTTT plugin, and processing the input consumes excessive CPU.

CVSS severity7.5
High
EPSS probability1.89%
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 Apprise before 0.9.5.1 allows remote attackers to hang a hosting process via a crafted IFTTT URL. NotifyIFTTT.parse_native_url applies nested, overlapping repetition to attacker-controlled event-path characters, causing excessive backtracking. The path is reachable when a publicly hosted application grants access to the bundled IFTTT plugin, and processing the input consumes excessive CPU.

The record

CVE
CVE-2021-39229
Published
Sep 20, 2021
Updated
Aug 4, 2024
Vendor
Chris Caron
Product
Apprise
Classifications
CWE-400, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 20, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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=< 0.9.5.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Chris Caron · Appriseversion=< 0.9.5.1

Published CVSS scores

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.

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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-400Uncontrolled Resource Consumption
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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