Blocklist bypass via leading-whitespace URL parsing
Published Feb 17, 2023 · Updated Nov 3, 2025
Improper URL parsing in Python before 3.11.4 allows remote attackers to bypass scheme or domain blocklists with leading whitespace. The urllib.parse urlsplit and urlparse functions preserve leading C0 controls and spaces, leaving the scheme and hostname empty while downstream consumers interpret the URL differently. Exposure requires security decisions based on those parsed fields before the attacker-controlled URL reaches a differing parser, enabling consumer-dependent SSRF, file reads, or command execution.
Summary
What happened
Improper URL parsing in Python before 3.11.4 allows remote attackers to bypass scheme or domain blocklists with leading whitespace. The urllib.parse urlsplit and urlparse functions preserve leading C0 controls and spaces, leaving the scheme and hostname empty while downstream consumers interpret the URL differently. Exposure requires security decisions based on those parsed fields before the attacker-controlled URL reaches a differing parser, enabling consumer-dependent SSRF, file reads, or command execution.
The record
- CVE
- CVE-2023-24329
- Published
- Feb 17, 2023
- Updated
- Nov 3, 2025
- Vendor
- Unknown vendor
- Product
- Unknown product
- Classifications
- CWE-20
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Feb 17, 2023CVE publishedPublication date reported by the CVE source.
- Nov 3, 2025Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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What is affected?
Affected products and versions are unavailable in this record.
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
- Leading-whitespace URL blocklist-bypass proof of conceptproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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