CVE-2026-45409
MediumCVSS 5.3Exploitation Probability (EPSS)
Low risk35th percentile - higher than 35% of all known CVEs
Summary
Python versions prior to 3.15 have an issue with the `idna.encode()` function that can be exploited to perform a denial-of-service attack by processing specially crafted arguments. High values of N in payloads can lead to long processing times.
Risk Assessment
Organizations may be vulnerable to denial-of-service attacks that can lead to significant resource consumption and potential application downtime.
Recommendation
It is recommended to upgrade to version 3.15 or later to take advantage of the fixes related to rejecting long inputs. Additionally, implement length validation for domain names before passing them to the `idna.encode()` function.
Original NVD description (English source)
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.