Connection redirection via percent-encoded delimiter injection in connection string hosts

PyMongo's connection string parsing decodes percent-encoded characters in the host portion before the host list is separated on its delimiters. When an application places a hostname value supplied by an unauthenticated party into a connection string, that party may cause additional servers of their choosing to be added to the application's database client. The application may then send its authentication exchange and database operations to one of those servers, which can observe limited information and return altered results.

Source published

24 Sep 2026 18:18:12 UTC

Source modified

24 Sep 2026 19:12:05 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · 8.3 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:H/VA:N/SC:N/SI:N/SA:N

CVSS 3.1 · 6.5 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:N