PT-2026-42782 · Pypi · Idna

Kc1Zs4 · Published 2026-05-22 · Updated 2026-05-22 · CVE-2026-39821

Positive Technologies (AI Summary)

Name of the Vulnerable Software and Affected Versions idna (affected versions not specified)

Description The ToASCII() and ToUnicode() functions incorrectly accept Punycode-encoded labels that decode to an ASCII-only label. For instance, ToUnicode("xn--example-.com") returns "example.com" instead of an error. This behavior can lead to privilege escalation in programs using the idna package; a program performing privilege checks on an ASCII hostname might reject "example.com" but permit "xn--example-.com", and subsequently granting access to "example.com" after converting the hostname to Unicode.

Recommendations At the moment, there is no information about a newer version that contains a fix for this vulnerability.

Related Identifiers

CVE-2026-39821

GO-2026-5026

Affected Products

Idna

References · 5

• https://osv.dev/vulnerability/GO-2026-5026 · Vendor Advisory
• https://pkg.go.dev/vuln/GO-2026-5026 · Note
• https://go.dev/cl/767220 · Note
• https://groups.google.com/g/golang-announce/c/iI-mYSI0lu8 · Note
• https://go.dev/issue/78760 · Note