# CVE-2026-40198: Net::CIDR::Lite versions before 0.23 for Perl does not validate IPv6 group count, which may allow IP ACL bypass

> Attackers can bypass IP-based access controls by providing malformed IPv6 addresses that cause incorrect range matching in the Net::CIDR::Lite Perl library.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/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-2026-40198, AZL-82739, DEBIAN-CVE-2026-40198, GHSA-c25q-mqx5-m6v8, UBUNTU-CVE-2026-40198

## What is CVE-2026-40198?

CVE-2026-40198 is a high-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 does not validate IPv6 group count, which may allow IP ACL bypass.

_pack_ipv6() does not check that uncompressed IPv6 addresses (without ::) have exactly 8 hex groups. Inputs like "abcd", "1:2:3", or "1:2:3:4:5:6:7" are accepted and produce packed values of wrong length (3, 7, or 15 bytes instead of 17).

The packed values are used internally for mask and comparison operations. find() and bin_find() use Perl string comparison (lt/gt) on these values, and comparing strings of different lengths gives wrong results. This can cause find() to incorrectly report an address as inside or outside a range.

Example:

  my $cidr = Net::CIDR::Lite->new("::/8");
  $cidr->find("1:2:3");  # invalid input, incorrectly returns true

This is the same class of input validation issue as CVE-2021-47154 (IPv4 leading zeros) previously fixed in this module.

See also CVE-2026-40199, a related issue in the same function affecting IPv4 mapped IPv6 addresses.

Weakness: CWE-1286 (Improper Validation of Syntactic Correctness of Input)

## Which versions are affected by CVE-2026-40198?

It affects 1 product.


Products: Stigtsp Net\.

## How do I fix CVE-2026-40198?

Upgrade to a fixed version.

## Is CVE-2026-40198 being exploited?

There is no known exploitation of CVE-2026-40198 in the wild and no public exploit code.

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

- [CVE-2026-40199](https://insights.sbomify.com/CVE-2026-40199/): Net::CIDR::Lite versions before 0.23 for Perl mishandles IPv4 mapped IPv6 addresses, which may allow IP ACL bypass (medium 6.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-40198 and fix it if it is affected.

What it is: CVE-2026-40198 is a high-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-2026-40198 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-2026-40198/ (Markdown: https://insights.sbomify.com/CVE-2026-40198/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-40198
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-40198
- OSV: https://osv.dev/vulnerability/CVE-2026-40198

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-40198/
Summaries are generated and may contain mistakes; the official description above is the record.