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
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.
INFO
Published Date :
Aug. 31, 2026, 6:17 p.m.
Last Modified :
Sept. 3, 2026, 4:41 p.m.
Remotely Exploit :
Yes !
Source :
9b29abf9-4ab0-4765-b253-1875cd9b441e
Affected Products
The following products are affected by CVE-2026-19953
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
No affected product recoded yet
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | MEDIUM | 134c704f-9b21-4f2e-91b3-4a467353bcc0 |
Solution
- Update Perl to version 5.36 or later.
- Verify URI handling and nameprep normalization.
- Use normalized hostnames for security decisions.
- Apply IDNA NFC normalization to host labels.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-19953.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-19953 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-19953
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-19953 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-19953 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Sep. 01, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N Added SSVC {'id': 'CVE-2026-19953', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'yes'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-09-01T15:16:46.820304Z'} -
CVE Modified by af854a3a-2127-422b-91ae-364da2661108
Aug. 31, 2026
Action Type Old Value New Value Added Reference http://www.openwall.com/lists/oss-security/2026/08/31/14 -
New CVE Received by 9b29abf9-4ab0-4765-b253-1875cd9b441e
Aug. 31, 2026
Action Type Old Value New Value Added 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. Added CWE CWE-1289 Added Affected New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/19xxx/CVE-2026-19953.json">CVE-2026-19953</a> Added Reference https://github.com/libwww-perl/URI/commit/956619a9e94f86d8d2c529b4e06a3674c54a73e7.patch Added Reference https://github.com/libwww-perl/URI/pull/191 Added Reference https://metacpan.org/release/OALDERS/URI-5.36/changes Added Reference https://www.rfc-editor.org/rfc/rfc5891#section-5.2