# 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.

- **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:** 31 Aug 2026
- **Updated:** 1 Sep 2026
- **Also known as:** ALSA-2026:84587, ALSA-2026:84588, ALSA-2026:84590, AZL-98562, BELL-CVE-2026-19953, DEBIAN-CVE-2026-19953, ECHO-21d4-7d4e-9762, GHSA-wf9v-63v3-ff2x, MGASA-2026-0445, OESA-2026-3588, OESA-2026-3589, OESA-2026-3590, OESA-2026-3591, OESA-2026-3714, RHSA-2026:84587, RHSA-2026:84588, RHSA-2026:84590, RLSA-2026:84587, RLSA-2026:84588, RLSA-2026:84590, SUSE-SU-2026:23633-1, SUSE-SU-2026:4046-1, SUSE-SU-2026:4070-1, UBUNTU-CVE-2026-19953, openSUSE-SU-2026:11663-1, openSUSE-SU-2026:21773-1

## 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 (Improper Validation of Unsafe Equivalence in Input)

## Which versions are affected by CVE-2026-19953?


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `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.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-19953 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-19953 in the wild and no public exploit code.

Affected product: perl-URI. 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-2026-19953/ (Markdown: https://insights.sbomify.com/CVE-2026-19953/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-19953
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-19953
- OSV: https://osv.dev/vulnerability/CVE-2026-19953

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-19953/
Summaries are generated and may contain mistakes; the official description above is the record.