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Response snapshot Oct 27, 2026, 16:31 UTC

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VulnerabilityCVE-2026-106435

MongoDB Python Driver: Out-of-bounds read in BSON decoding via a malformed Regex element

MongoDB Python Driver: Out-of-bounds read in BSON decoding via a malformed Regex element

Published Updated

At a glance

Exploited
Not known
Severity
8.2 High (CVSS 4.0)
Chance of exploitation
Not estimated
Sources
1 source

What to do

GitHub lists first patched versions: pymongo: 4.18.3. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-98qm-wvgf-w4cf (opens a new tab)

What happened

### Impact The C extension's BSON decoder scans a Regex element's pattern and flags strings with strlen before checking the document's remaining length, so a crafted truncated Regex element can read past the end of the caller's buffer. bson.decode and bson.decode_all accept mmap and array buffers, which carry no NUL sentinel; the read can cross into unmapped memory and kill the process with an uncatchable SIGSEGV.

Any application decoding untrusted BSON from such buffers is affected — impact is availability only, since the out-of-bounds bytes are never returned as content. NUL-terminated buffers (bytes, bytearray) raise `InvalidBSON` at worst; the driver's own transport and pure-Python installs are not affected. All releases through 4.18.2 are affected when the C extension is loaded.

### Patches Fixed in PyMongo 4.18.3. Malformed Regex elements now raise InvalidBSON on every accepted buffer type; valid documents decode unchanged.

### Workarounds Decode untrusted BSON only from NUL-terminated buffers — bytes or bytearray — and copy mmap input first, e.g. bytes(mm[:size]).

Continue reading

Affected package ranges reported by GitHub: pymongo: >= 3.9.0, <= 4.18.2

Scores and how they were measured

CVSS base severity

8.2

Version 4.0As of

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

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

Not available

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-98qm-wvgf-w4cf (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-98qm-wvgf-w4cf, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 27). MongoDB Python Driver: Out-of-bounds read in BSON decoding via a malformed Regex element (CVE-2026-106435). https://kevwire.com/record/CVE-2026-106435

MLA

"MongoDB Python Driver: Out-of-bounds read in BSON decoding via a malformed Regex element (CVE-2026-106435)." KEVWire, 27 Oct. 2026, kevwire.com/record/CVE-2026-106435.

Chicago

KEVWire. "MongoDB Python Driver: Out-of-bounds read in BSON decoding via a malformed Regex element (CVE-2026-106435)." Last modified October 27, 2026. https://kevwire.com/record/CVE-2026-106435.

Evidence summary (plain text)

MongoDB Python Driver: Out-of-bounds read in BSON decoding via a malformed Regex element (Oct 27, 2026).
MongoDB Python Driver: Out-of-bounds read in BSON decoding via a malformed Regex element
CVSS 8.2 (version 4.0; evidence as of Oct 27, 2026; https://github.com/advisories/GHSA-98qm-wvgf-w4cf).
Sources:
GitHub-reviewed advisory GHSA-98qm-wvgf-w4cf: https://github.com/advisories/GHSA-98qm-wvgf-w4cf
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
Record ID: CVE-2026-106435.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 27, 2026, 16:25 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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Record details

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