IP ACL bypass via zero-padded CIDR masks
Published May 10, 2026 · Updated May 10, 2026
Improper CIDR mask validation in Stig Palmquist Net::CIDR::Lite before 0.24 allows attackers to bypass IP ACLs via crafted masks. Net::CIDR::Lite::add accepts mask strings such as /00 and /01 because its digit-only check permits leading zeros, then coerces them to the same numeric prefix as /0 and /1. Exploitation requires a consuming application to accept attacker-controlled CIDR masks and rely on textual filtering or ACL logic that distinguishes padded input from its parsed range.
Summary
What happened
Improper CIDR mask validation in Stig Palmquist Net::CIDR::Lite before 0.24 allows attackers to bypass IP ACLs via crafted masks. Net::CIDR::Lite::add accepts mask strings such as /00 and /01 because its digit-only check permits leading zeros, then coerces them to the same numeric prefix as /0 and /1. Exploitation requires a consuming application to accept attacker-controlled CIDR masks and rely on textual filtering or ACL logic that distinguishes padded input from its parsed range.
The record
- CVE
- CVE-2026-45191
- Published
- May 10, 2026
- Updated
- May 10, 2026
- Vendor
- Stig Palmquist
- Product
- Net::CIDR::Lite
- Classifications
- CWE-1289
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- May 10, 2026CVE publishedPublication date reported by the CVE source.
- May 10, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=0 <0.24
What conditions does exploitation require?
What is affected?
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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