CVE-2026-19953 URI versions before 5.36 for Perl encode non-NFC host names to non-standard punycode labels via missing normalization in nameprep.
Attackers can bypass host-based security checks like SSRF filters or allowlists by exploiting Unicode normalization flaws in URI parsing.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-19953?
CVE-2026-19953 is a medium-severity vulnerability in perl-URI, published on 31 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
URI versions before 5.36 for Perl encode non-NFC host names to non-standard punycode labels via missing normalization in nameprep.
nameprep lowercases each host label but performs no Unicode normalization. IDNA requires a label to be normalized to Form C before it is encoded (RFC 5891), so a label that is not already in NFC is encoded to a different A-label than its normalized form. A label built from the precomposed Devanagari sequence U+0958 U+093E encodes to xn--72b5c without normalization but to xn--11b2fg after NFC normalization, and xn--72b5c does not round-trip back to the original label.
Any caller that reads host() from a URI built from untrusted input and uses it for a security decision (an allow or deny list, an SSRF filter, deduplication, a cache key) sees the non-standard label, while a client that fetches the same URL resolves the NFC form, so the check and the fetch can disagree about the host.
Weakness: CWE-1289
Which versions are affected by CVE-2026-19953?
Linux distribution packages (15)
perl-URI AlmaLinux:10 | All versions | 5.27-3.el10_2.1 |
perl-URI AlmaLinux:8 | All versions | 1.73-4.el8_10 |
perl-URI AlmaLinux:9 | All versions | 5.09-3.el9_8.1 |
perl-URI Red Hat:enterprise_linux:10.2 | All versions | 0:5.27-3.el10_2.1 |
perl-URI Red Hat:enterprise_linux:8::baseos | All versions | 0:1.73-4.el8_10 |
perl-URI Red Hat:enterprise_linux:9::appstream | All versions | 0:5.09-3.el9_8.1 |
perl-URI Rocky Linux:10 | All versions | 0:5.27-3.el10_2.1 |
perl-URI Rocky Linux:8 | All versions | 0:1.73-4.el8_10 |
perl-URI Rocky Linux:9 | All versions | 0:5.09-3.el9_8.1 |
perl-URI SUSE:Linux Enterprise Module for Basesystem 15 SP7 | All versions | 1.73-150000.3.3.1 |
perl-URI SUSE:Linux Enterprise Server 16.0 | All versions | 5.310.0-160000.3.1 |
perl-URI SUSE:Linux Enterprise Server LTSS Extended Security 12 SP5 | All versions | 1.60-9.3.1 |
perl-URI SUSE:Linux Enterprise Server for SAP applications 16.0 | All versions | 5.310.0-160000.3.1 |
perl-URI openSUSE:Leap 16.0 | All versions | 5.310.0-160000.3.1 |
perl-URI openSUSE:Tumbleweed | All versions | 5.360.0-1.1 |
How do I fix CVE-2026-19953?
Upgrade to a fixed version.
Is CVE-2026-19953 being exploited?
There is no known exploitation of CVE-2026-19953 in the wild and no public exploit code.
Sources
Also known as ALSA-2026:84587, ALSA-2026:84588, ALSA-2026:84590, AZL-98562, BELL-CVE-2026-19953, DEBIAN-CVE-2026-19953 and 20 more.