CVE-2026-39821
Invoking failure to reject ASCII-only Punycode-encoded labels in golang.org/x/net/idna
- Published
- May 22, 2026
- Updated
- Sep 17, 2026
- Assigning CNA
- Go
- Evidence observed
- Oct 23, 2026
Primary CVSS
nvd · CVSS 3.1
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:NLow · next 30 days
- Percentile
- 52.2%
- Model date
- Oct 21, 2026
EPSS is a statistical estimate, not a certainty or a measure of impact. Combine it with CVSS, KEV status, exposure and your environment.
Summary
The ToASCII and ToUnicode functions incorrectly accept Punycode-encoded labels that decode to an ASCII-only label. For example, ToUnicode("xn--example-.com") incorrectly returns the name "example.com" rather than an error. This behavior can lead to privilege escalation in programs using the idna package. For example, a program which performs privilege checks on the ASCII hostname may reject "example.com" but permit "xn--example-.com". If that program subsequently converts the ASCII hostname to Unicode, it will inadvertently permits access to the Unicode name "example.com".
Sources
CVE proof-of-concept labs, exploit scripts, and detection/prevention rules (Nginx, Apache, Snort, YARA) for high-severity CVEs. Authorized security testing & research only.
Responsible use
Use vulnerability information only on systems you own or are authorized to test. Kitploit links to public research metadata and does not store exploit code or malicious payloads.