kjd idna up to 3.14 Compatibility idna.encode redos

Summaryinfo

A vulnerability, which was classified as problematic, was found in kjd idna up to 3.14. Affected by this vulnerability is the function idna.encode of the component Compatibility Handler. Executing a manipulation can lead to redos. This vulnerability appears as CVE-2026-45409. The attack may be performed from remote. There is no available exploit. You should upgrade the affected component.

Detailsinfo

A vulnerability classified as problematic was found in kjd idna up to 3.14. This vulnerability affects the function idna.encode of the component Compatibility Handler. The manipulation with an unknown input leads to a redos vulnerability. The CWE definition for the vulnerability is CWE-1333. The product uses a regular expression with an inefficient, possibly exponential worst-case computational complexity that consumes excessive CPU cycles. As an impact it is known to affect availability. CVE summarizes:

Internationalized Domain Names in Applications (IDNA) for Python provides support for Internationalized Domain Names in Applications (IDNA) and Unicode IDNA Compatibility Processing. In versions prior to 3.15, payloads such as `"\u0660" * N` or `"\u30fb" * N + "\u6f22"` utilize the `valid_contexto` function prior to length rejection, and for high values of `N` will take a long time to process. This is the same issue as CVE-2024-3651, however the original remediation in 2024 was not a complete fix. A specially crafted argument to the `idna.encode()` function could consume significant resources. This may lead to a denial-of-service. Starting in version 3.14, the function rejects long inputs as soon as practicable prior to any further processing to minimize resource consumption. In version 3.15, this approach was extended to lesser used alternate functions (i.e. per-label conversions and codec support). A workaround is available. Domain names cannot exceed 253 characters in length. If this length limit is enforced prior to passing the domain to the `idna.encode()` function, it should no longer consume significant resources. This is triggered by arbitrarily large inputs that would not occur in normal usage, but may be passed to the library assuming there is no preliminary input validation by the higher-level application.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-45409 since 05/12/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1449.003.

The vulnerability scanner Nessus provides a plugin with the ID 319607 (Linux Distros Unpatched Vulnerability : CVE-2026-45409), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 3.15 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at Tenable (319607). Once again VulDB remains the best source for vulnerability data.

Productinfo

Vendor

• kjd

Name

• idna

Version

• 3.0
• 3.1
• 3.2
• 3.3
• 3.4
• 3.5
• 3.6
• 3.7
• 3.8
• 3.9
• 3.10
• 3.11
• 3.12
• 3.13
• 3.14

Website

• Product: https://github.com/kjd/idna/

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Once again VulDB remains the best source for vulnerability data.

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