Service interruption via quadratic joiner-context scans
Published Jul 7, 2024 · Updated Nov 4, 2025
Resource exhaustion in Kim Davies idna before 3.7 allows attackers to interrupt services through oversized input to idna.encode(). For each joiner, valid_contextj scans adjacent characters across the label, so repeated joiners make processing time grow quadratically. Exploitation requires a consuming application to pass an arbitrarily large, attacker-controlled domain string without enforcing the 253-character limit.
Summary
What happened
Resource exhaustion in Kim Davies idna before 3.7 allows attackers to interrupt services through oversized input to idna.encode(). For each joiner, valid_contextj scans adjacent characters across the label, so repeated joiners make processing time grow quadratically. Exploitation requires a consuming application to pass an arbitrarily large, attacker-controlled domain string without enforcing the 253-character limit.
The record
- CVE
- CVE-2024-3651
- Published
- Jul 7, 2024
- Updated
- Nov 4, 2025
- Vendor
- Kim Davies
- Product
- idna
- Classifications
- CWE-400, T1499.004
- Attack vector
- local
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jul 7, 2024CVE publishedPublication date reported by the CVE source.
- Nov 4, 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.
- Affected versionversion=unspecified <3.7
What conditions does exploitation require?
What is affected?
Published CVSS scores
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.
Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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