CVSS 3.1
9.6 criticalCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:NCVE-2026-39821
Critical (9.6) in golang net. EPSS 1.8% chance of exploitation in the next 30 days. Fixed in stdlib 1.25.13, 1.26.6, 1.27.0-rc.3.
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".
Severity
- EPSS
- 1.8% chance of exploitation in the next 30 days; higher than 78% of CVEs (scores of 2026-10-31)
- CWE
- CWE-1289
- Published
- Modified
- Record from
- the NVD, synced
Affected
- golang:net
Packages (OSV)
| Advisory | Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|---|
| GO-2026-5026 | Go | stdlib | <1.25.13 >=1.26.0-0 <1.26.6 >=1.27.0-0 <1.27.0-rc.3 | 1.25.13, 1.26.6, 1.27.0-rc.3 |
| GO-2026-5026 | Go | golang.org/x/net | <0.55.0 | 0.55.0 |