CVE-2026-19566 Denial of service in Net::CIDR::Set
Attackers can cause memory exhaustion or corrupt CIDR sets by supplying unbounded IPv6 prefix lengths to Net::CIDR::Set functions.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-19566?
CVE-2026-19566 is a high-severity denial of service vulnerability in RRWO Net::CIDR::Set, published on 12 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Net::CIDR::Set versions before 0.23 for Perl allow memory exhaustion and malformed set ranges via unbounded IPv6 prefix lengths.
The _encode method accepts any prefix length matching `(0|[1-9][0-9]*)` and passes it to _width2bits(), which builds the mask as `'1' x ($width + 8)`, one character per bit. The _inc() method then unpacks the packed mask into a Perl array of one scalar per byte, so the prefix length alone sets the allocation size: `::/100000000` builds a 100 MB string and a 12.5 million element array. The value being tested is parsed, not just the configured ranges: contains() builds a set from its argument, and _guess_coder() tries the IPv4 coder and then the IPv6 coder, so an IPv4-only set expands an oversized IPv6 prefix length before the mixed address width check rejects it.
Any caller that passes untrusted input to contains() or add() can exhaust process memory. A prefix length above 128 is also stored as a range that does not match the requested block: 2001:db8::/129 stringifies back unchanged, contains() of its own base address returns false, and removing it from a set drops the base address while the set still prints as covering it.
Which versions are affected by CVE-2026-19566?
Linux distribution packages (1)
perl-Net-CIDR-Set openSUSE:Tumbleweed | All versions | 0.230.0-1.1 |
How do I fix CVE-2026-19566?
Upgrade to a fixed version.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-19566 being exploited?
There is no known exploitation of CVE-2026-19566 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-19566, GHSA-grjr-r4x5-mx4p, UBUNTU-CVE-2026-19566, openSUSE-SU-2026:11550-1.