# CVE-2026-40199: libnet-cidr-lite-perl: Net::CIDR::Lite versions before 0.23 for Perl mishandles IPv4 mapped IPv6 addresses, which may allow IP ACL bypass

CVE-2026-40199 is fixed in 2 products on 1 platform, first by libnet-cidr-lite-perl 0.21-1ubuntu0.18.04.1~esm1, released April 10, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-40199
- Priority: Routine
- CVSS: 6.5 (medium)
- EPSS: 0.0031
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Apr 10, 2026

## Description

Net::CIDR::Lite versions before 0.23 for Perl mishandles IPv4 mapped IPv6 addresses, which may allow IP ACL bypass.  _pack_ipv6() includes the sentinel byte from _pack_ipv4() when building the packed representation of IPv4 mapped addresses like ::ffff:192.168.1.1. This produces an 18 byte value instead of 17 bytes, misaligning the IPv4 part of the address.  The wrong length causes incorrect results in mask operations (bitwise AND truncates to the shorter operand) and in find() / bin_find() which use Perl string comparison (lt/gt). This can cause find() to incorrectly match or miss addresses.  Example:    my $cidr = Net::CIDR::Lite->new("::ffff:192.168.1.0/120");   $cidr->find("::ffff:192.168.2.0");  # incorrectly returns true  This is triggered by valid RFC 4291 IPv4 mapped addresses (::ffff:x.x.x.x).  See also CVE-2026-40198, a related issue in the same function affecting malformed IPv6 addresses.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | libnet-cidr-lite-perl Debian 12.15 (bookworm) | 0.22-3~deb12u1 | [DEBIAN-CVE-2026-40199](https://patchblox.com/security/data/fix/linux/debian-cve-2026-40199.md) | Apr 10, 2026 |
| Linux | libnet-cidr-lite-perl Debian 13.5 (trixie) | 0.22-3~deb13u1 | [DEBIAN-CVE-2026-40199](https://patchblox.com/security/data/fix/linux/debian-cve-2026-40199.md) | Apr 10, 2026 |
| Linux | libnet-cidr-lite-perl Debian 14 | 0.22-3 | [DEBIAN-CVE-2026-40199](https://patchblox.com/security/data/fix/linux/debian-cve-2026-40199.md) | Apr 10, 2026 |
| Linux | libnet-cidr-lite-perl Ubuntu 18.04.6 LTS (bionic) | 0.21-1ubuntu0.18.04.1~esm1 | [libnet-cidr-lite-perl 0.21-1ubuntu0.18.04.1~esm1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-libnet-cidr-lite-perl-0.21-1ubuntu0.18.04.1-esm1.md) | Apr 10, 2026 |
| Linux | libnet-cidr-lite-perl Ubuntu 20.04 LTS (focal) | 0.21-2ubuntu0.1+esm1 | [libnet-cidr-lite-perl 0.21-2ubuntu0.1+esm1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-libnet-cidr-lite-perl-0.21-2ubuntu0.1-esm1.md) | Apr 10, 2026 |
| Linux | libnet-cidr-lite-perl Ubuntu 22.04.1 LTS (jammy) | 0.22-1ubuntu0.1 | [libnet-cidr-lite-perl 0.22-1ubuntu0.1](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-libnet-cidr-lite-perl-0.22-1ubuntu0.1.md) | Apr 10, 2026 |
| Linux | libnet-cidr-lite-perl Ubuntu 24.04.5 LTS (noble) | 0.22-2ubuntu0.24.04.1 | [libnet-cidr-lite-perl 0.22-2ubuntu0.24.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-noble-libnet-cidr-lite-perl-0.22-2ubuntu0.24.04.1.md) | Apr 10, 2026 |
| Linux | libnet-cidr-lite-perl Ubuntu 25.10 (questing) | 0.22-2ubuntu0.25.10.1 | [libnet-cidr-lite-perl 0.22-2ubuntu0.25.10.1](https://patchblox.com/security/data/fix/linux/ubuntu-questing-libnet-cidr-lite-perl-0.22-2ubuntu0.25.10.1.md) | Apr 10, 2026 |
| Linux | libnet-cidr-lite-perl Ubuntu 26.04.1 LTS (resolute) | 0.22-2ubuntu0.26.04.1 | [libnet-cidr-lite-perl 0.22-2ubuntu0.26.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-libnet-cidr-lite-perl-0.22-2ubuntu0.26.04.1.md) | Apr 10, 2026 |
| Linux | perl-Net-CIDR-Lite amzn 2023 | 0.22-8.amzn2023.0.1 | [ALAS2023-2026-1624](https://patchblox.com/security/data/fix/linux/alas2023-2026-1624.md) | Apr 27, 2026 |

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