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CVE-2026-45409— Internationalized Domain Names in Applications (IDNA): Specially crafted inputs to idna.encode() can bypass CVE-2024-3651 fix

Quick assessment

Affected
kjd idna
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Internationalized Domain Names in Applications是Kim Davies个人开发者的一个国际化域名编码与解码工具。 Internationalized Domain Names in Applications 3.15之前版本存在安全漏洞，该漏洞源于valid_contexto函数在长度拒绝之前处理特定有效载荷，可能导致处理时间过长，消耗大量资源，导致拒绝服务。

AI Predicted 5.3 Difficulty: Easy EPSS 0.46% · P39

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking

Affected Version Matrix 1

VendorProduct Version RangeStatus
kjd idna < 3.15 affected
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I. Basic Information for CVE-2026-45409

Vulnerability Information
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Vulnerability Title
Internationalized Domain Names in Applications (IDNA): Specially crafted inputs to idna.encode() can bypass CVE-2024-3651 fix
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
CWE-1333
Source: CVE Program / CVE List V5
Vulnerability Title
Internationalized Domain Names in Applications 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Internationalized Domain Names in Applications是Kim Davies个人开发者的一个国际化域名编码与解码工具。 Internationalized Domain Names in Applications 3.15之前版本存在安全漏洞，该漏洞源于valid_contexto函数在长度拒绝之前处理特定有效载荷，可能导致处理时间过长，消耗大量资源，导致拒绝服务。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
kjd idna < 3.15 -

II. Public POCs for CVE-2026-45409

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III. Intelligence Information for CVE-2026-45409

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Vendor Advisories for CVE-2026-45409 (1)

IV. Related Vulnerabilities

Same vendor: kjd
Same weakness: CWE-1333

V. Comments for CVE-2026-45409

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