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High, CVSS 8.3amended

PyMongo: PYTHON-5986 Host injection in PyMongo connection string parsing via percent-encoded delimiters

CVE-2026-96748GHSA-vp6j-j7w5-5xjj

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (pymongo 4.18.2), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • PyPI pymongo

    Affected
    >= 3.5.0, <= 4.18.1
    Fixed in
    4.18.2

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
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 · score source
EPSS
  • CVE-2026-96748: 0.36% estimated exploitation activity in the next 30 days; percentile 29.92 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary PyMongo percent-decoded the entire host section of a connection string before splitting it into individual host:port entries. A percent-encoded , or : in a hostname therefore decoded into a real delimiter, injecting an additional attacker-chosen host and port into the client's seed list. Impact An application that interpolates untrusted input into a MongoDB connection string -- for example, a tenant name or hostname fragment taken from a request -- could be made to add an attacker-controlled server to the seed list. Because %2C and %3A survive most URL-safety checks and only become delimiters inside PyMongo's parser, input that looks like a single hostname to the application becomes two hosts to the driver. The client may then perform topology discovery and authentication against the attacker's host, exposing credentials, or route operations to it. Unix domain socket paths, the only host identifiers that legitimately require percent-encoding, are not affected. Patches Fixed…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 4 · amended ·

    Amended from ghsa record GHSA-vp6j-j7w5-5xjj

  2. Revision 3 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  3. Revision 2 · amended ·

    Amended from osv record GHSA-vp6j-j7w5-5xjj

  4. Revision 1 · created ·

    Published from ghsa record GHSA-vp6j-j7w5-5xjj

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-96748

Advisory: PyMongo: PYTHON-5986 Host injection in PyMongo connection string parsing via percent-encoded delimiters
IDs: CVE-2026-96748, GHSA-vp6j-j7w5-5xjj
Record: https://patchnext.com/advisories/cve-2026-96748 (revision 4, source checked 26 Oct 2026, 13:55 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: pymongo 4.18.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI pymongo: affected >= 3.5.0, <= 4.18.1; fixed in 4.18.2

## Suggested inspection (read-only)
- `python -m pip show pymongo`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on pymongo.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-vp6j-j7w5-5xjj (GitHub-reviewed advisory GHSA-vp6j-j7w5-5xjj lists affected ranges: PyPI pymongo >=3.5.0 <=4.18.1)
- Verified: https://osv.dev/vulnerability/GHSA-vp6j-j7w5-5xjj (OSV record GHSA-vp6j-j7w5-5xjj lists affected ranges: PyPI pymongo >=3.5.0 <4.18.2 (fixed))

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