vulnerability / NVI-00011779 / Revision 4
PyMongo: PYTHON-5986 Host injection in PyMongo connection string parsing via percent-encoded delimiters
GitHub lists this reviewed advisory for pymongo. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
6.5 high
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
6.5 MEDIUM (3.1)
cna@mongodb.com severity; no combined Null risk score.
8.3 HIGH (4.0)
cna@mongodb.com severity; no combined Null risk score.
0.361%
FIRST EPSS model v2026.06.15; exploitation probability over 30 days, percentile 0.30025. Missing scores are unknown.
As of · FIRST EPSS
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
pymongo
source listed>= 3.5.0, <= 4.18.1
### 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 in PyMongo 4.18.2. Percent-decoding was moved into `split_hosts` and now applies only to Unix domain socket paths, identified by an unescaped `.sock` suffix before decoding, a
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. FIRST EPSS
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
- NVD lastModified does not establish freshness of every associated CPE record.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-vp6j-j7w5-5xjj ↗
GitHub Advisory Database · vendor advisory
Observed . GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.
- CVE-2026-96748 ↗
NIST National Vulnerability Database · official catalog
Observed . This product uses data from the NVD API but is not endorsed or certified by the NVD.
- CVE-2026-96748 ↗
FIRST EPSS · official catalog
Observed . FIRST EPSS; probability of exploitation in the next 30 days, not local compromise. Dataset date/model retained; FIRST services terms apply.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 4 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 2 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.