Improper Handling of URL Encoding (Hex Encoding) Affecting pymongo package, versions [3.5.0,4.18.2)
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-PYTHON-PYMONGO-20158849
- published27 Sept 2026
- disclosed24 Sept 2026
- creditUnknown
Introduced: 24 Sep 2026
NewCVE-2026-96748 (opens in a new tab)How to fix?
Upgrade pymongo to version 4.18.2 or higher.
Overview
Affected versions of this package are vulnerable to Improper Handling of URL Encoding (Hex Encoding) in _validate_uri and _parse_srv, which apply unquote_plus to the entire host section of a connection string before splitting it on , and :, so a percent-encoded delimiter decodes into a real one. An attacker can add a server they control to the client's seed list, which then receives topology discovery and authentication attempts carrying the application's credentials, by supplying a value containing %2C or %3A where the application interpolates untrusted input such as a tenant name or hostname fragment into the URI. This requires the application to build its connection string from request data, and Unix domain socket paths, the one host form that legitimately needs percent-encoding, are not affected.