CVE-20XX-?
agent?

CVE-2026-39821

9.6 CRITICAL 2% exploit odds Fix listed Auth & access Library

What it is

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".

At a glance

Exploitability
Can be exploited over the network with a low-privilege account. High risk of data exposure, data tampering.
Exploit odds
1.8% chance of exploitation in the next 30 days (EPSS).
Fix
A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

  1. PublishedDisclosed publicly on CVE.org and NVD
  2. Last updatedMost recent change to the record

Why it ranks here

Details

Published
Last modified
Exploit probability
1.8% · EPSS, next 30 days
Weakness
CWE-1289
Record status
Modified

Affected

Attack profile CVSS 3.1 · 9.6

Attack vector
Network
Complexity
Low
Privileges needed
Low
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
None
Raw vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2026-39821.md and follow it. Check whether this project is affected by CVE-2026-39821. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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Fix and advisories

References

NVD record · CVE.org record