CVE-2026-55859 is a medium-severity (CVSS 5.9) CWE-116 vulnerability in org.mariadb:r2dbc-mariadb. O3 Security confirms whether CVE-2026-55859 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
org.mariadb:r2dbc-mariadb has Inappropriate Encoding for Output Context and Improper Encoding or Escaping of Output
Real-World Exposure
org.mariadb:r2dbc-mariadbReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
Description
Summary
The connector encodes and decodes all character data assuming the connection character set is UTF-8. A server can change character_set_client mid-session to a non-UTF-8 charset, after which the driver and server interpret the same bytes under different encodings, causing silent data corruption and a client/server charset-confusion mismatch.
Details
The driver encodes and decodes all character data on the assumption that the connection character set is UTF-8. The server can, however, announce a change of character_set_client mid-session through the OK-packet session-state-tracking mechanism, for example via a SET NAMES … run by a stored routine or trigger, by server configuration, or by a hostile server.
If the new charset is not UTF-8, the driver continues to read and write UTF-8 while the server interprets the same bytes under a different encoding. The result is silent data corruption and a client/server charset-confusion mismatch. Charset confusion of this kind is also the primitive that can defeat byte-wise quoting/escaping when client and server disagree on a multi-byte encoding.
Am I affected?
You are affected if you use mariadb Connector/R2DBC (org.mariadb:r2dbc-mariadb) below 1.4.1 and a connection can be steered, by a hostile or man-in-the-middle server, or by server-side state such as a stored routine, trigger, or configuration — to switch character_set_client to a non-UTF-8 value mid-session.
Impact
Silent data corruption and a client/server encoding mismatch once the connection's charset diverges from UTF-8. Because the mismatch undermines the assumption that quoting/escaping operates on UTF-8 bytes, it belongs to the charset-confusion class that can lead to SQL injection.
Patches
Fixed in 1.4.1. Once the connection is fully initialized, any subsequent charset change to a value that is not utf8 / utf8mb3 / utf8mb4 is rejected: the driver raises R2dbcNonTransientResourceException (SQLState 08000) and closes the connection rather than continuing to exchange data under a mismatched encoding. Upgrade to 1.4.1 or later.
Workarounds
There is no reliable application-level workaround; upgrade to 1.4.1 or later.
Credit
Reported by Yalguun Tumenkhuu (@fg0x0).
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | org.mariadb:r2dbc-mariadb | all versions | 1.4.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.mariadb:r2dbc-mariadb. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update org.mariadb:r2dbc-mariadb to 1.4.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-55859 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-55859 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-55859. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-55859 in your dependencies?
O3 detects CVE-2026-55859 across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.