CVE-2026-19953Network attack vector

Host validation bypass via non-normalized IDNA labels

Published Aug 31, 2026 · Updated Sep 1, 2026

Improper input validation in libwww-perl URI before 5.36 allows context-dependent attackers to bypass host checks via non-NFC names. URI::_idna::nameprep lowercases each label but omits NFC normalization, producing a nonstandard A-label that disagrees with downstream clients. Exposure requires a caller to use host() on untrusted input for an allowlist, denylist, SSRF filter, routing decision, deduplication key, or cache key.

CVSS severity6.9
Medium
EPSS probability0.37%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Improper input validation in libwww-perl URI before 5.36 allows context-dependent attackers to bypass host checks via non-NFC names. URI::_idna::nameprep lowercases each label but omits NFC normalization, producing a nonstandard A-label that disagrees with downstream clients. Exposure requires a caller to use host() on untrusted input for an allowlist, denylist, SSRF filter, routing decision, deduplication key, or cache key.

The record

CVE
CVE-2026-19953
Published
Aug 31, 2026
Updated
Sep 1, 2026
Vendor
libwww-perl
Product
URI
Classifications
CWE-1289
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 31, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 1, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <5.36

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

libwww-perl · URIversion=0 <5.36

Published CVSS scores

6.9SUSECVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:L
6.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
5.3SUSECVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-1289Improper Validation of Unsafe Equivalence in Input

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo