CVE-2026-106431 — One-byte heap buffer overflow in BSON bulk document writer in MongoDB C Driver
An off-by-one error in the BSON bulk document writer in the MongoDB C Driver can write one zero byte immediately past a heap allocation when a document ends at a specific buffer boundary. An actor who can influence the size of documents serialized by an embedding application can corrupt adjacent process memory or terminate the process. Reaching this issue requires the application to use the BSON bulk-writer API and produce a precise cumulative document size.
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- EPSS 0.1% (30-day exploitation probability)+0
- Technical severity (medium)+3
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
CISA SSVC assessment CISA
Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Mongodb C Driver).
- No fix documented in the sources: reduce exposure and monitor the vendor advisory.
- Search available logs for exploit probes matching the vulnerability class (memory corruption), errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
Every base score collected
Sources score independently and may disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Scored by |
|---|---|---|---|---|---|
| 5.9 | CVSS 4.0 | Medium | — | — | cna@mongodb.com via NIST National Vulnerability Database |
| 5.9 | CVSS 4.0 | Medium | — | — | mongodb via CVE Program (cve.org) e CISA ADP |
| 5.7 | CVSS 3.1 | Medium | 1.4 | 4.2 | cna@mongodb.com via NIST National Vulnerability Database |
| 5.7 | CVSS 3.1 | Medium | — | — | mongodb via CVE Program (cve.org) e CISA ADP |
CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H (score shown at the top: cna@mongodb.com) Weakness MITRE
Weakness class according to MITRE’s CWE catalog.
EPSS over time FIRST
Oct 13, 2026 → Oct 15, 2026 · 3 reading(s) · max 0.10%
Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Local/physical vector: focus on endpoint telemetry (EDR) from affected hosts.
- Correlate service crashes/restarts with inbound traffic; repeated crashes may indicate attempts.
Timeline
What happened to this CVE, newest first.
- 2026
- Affected products added · mongodb/c driver
- SSVC assessment updated
- Record published
- CVSS changed · 5.7
- Source status changed · → Undergoing Analysis
- Record created in this database
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 1× Official description updated · Oct 13, 2026 – Oct 13, 2026
References
1 on the record
Elsewhere on this site
Related CVEs (same products)
- Medium CVE-2026-106437 Out-of-bounds read and write via undersized BSON buffer reservation in MongoDB C Driver 8d
- Medium CVE-2026-106438 Silent Decimal128 value corruption via incorrect exactness check in MongoDB C Driver 8d
- Medium CVE-2026-106430 Query and rename target confusion via embedded NUL truncation in MongoDB C++ Driver 8d
- Low CVE-2026-106428 Out-of-bounds read in SCRAM response parsing in MongoDB C Driver 8d
- Medium CVE-2026-96746 Heap buffer overflow via mid-scan command list growth in client topology monitoring 22d
- Low CVE-2026-93394 libmongoc SCRAM client nonce-validation bypass 29d
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No fixed version, patch or mitigation documented.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2026-106431 is "One-byte heap buffer overflow in BSON bulk document writer in MongoDB C Driver", rated Medium. It affects C Driver (Mongodb); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 5.7 describes technical severity. EPSS 0.10% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
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