Incomplete List of Disallowed Inputs Affecting cpython package, versions [0,]
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-CONAN-CPYTHON-15091538
- published25 Jan 2026
- disclosed21 Jan 2026
- creditUnknown
Introduced: 21 Jan 2026
NewCVE-2025-12781 (opens in a new tab)How to fix?
A fix was pushed into the master branch but not yet published.
Overview
Affected versions of this package are vulnerable to Incomplete List of Disallowed Inputs in the b64decode, standard_b64decode, and urlsafe_b64decode functions when the altchars parameter is used. An attacker can cause logical errors or compromise data integrity by submitting input containing the '+' and '/' characters, which are incorrectly accepted even when an alternative alphabet is specified.
Note: This is only exploitable if the application uses the base64 functions with an alternative alphabet via the altchars parameter and relies on these functions for input validation without additional checks.
Workaround
This vulnerability can be mitigated by implementing manual input validation before calling the base64 functions with an alternative alphabet, ensuring to reject any string containing the standard base64 characters, such as '+' and '/', that are not part of the expected alphabet.