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

> Attackers can bypass IP-based access controls by exploiting incorrect handling of IPv4-mapped IPv6 addresses in the Net::CIDR::Lite Perl library.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 10 Apr 2026
- **Updated:** 13 Apr 2026
- **Also known as:** ALPINE-CVE-2026-40199, AZL-82742, DEBIAN-CVE-2026-40199, GHSA-932w-96j4-j35v, UBUNTU-CVE-2026-40199

## What is CVE-2026-40199?

CVE-2026-40199 is a medium-severity vulnerability in STIGTSP Net::CIDR::Lite, published on 10 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-130 (Improper Handling of Length Parameter Inconsistency)

## Which versions are affected by CVE-2026-40199?

It affects 1 product.


Products: Stigtsp Net\.

## How do I fix CVE-2026-40199?

Upgrade to a fixed version.

## Is CVE-2026-40199 being exploited?

There is no known exploitation of CVE-2026-40199 in the wild and no public exploit code.

## Other vulnerabilities in STIGTSP Net::CIDR::Lite

- [CVE-2026-40198](https://insights.sbomify.com/CVE-2026-40198/): Net::CIDR::Lite versions before 0.23 for Perl does not validate IPv6 group count, which may allow IP ACL bypass (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-40199 and fix it if it is affected.

What it is: CVE-2026-40199 is a medium-severity vulnerability in STIGTSP Net::CIDR::Lite, published on 10 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-40199 in the wild and no public exploit code.

Affected product: STIGTSP Net::CIDR::Lite. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-40199/ (Markdown: https://insights.sbomify.com/CVE-2026-40199/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-40199
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-40199
- OSV: https://osv.dev/vulnerability/CVE-2026-40199

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-40199/
Summaries are generated and may contain mistakes; the official description above is the record.