How severe is CVE-2026-55859?

CVE-2026-55859 has a CVSS score of 5.9/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2026-55859?

CVE-2026-55859 affects the following packages: org.mariadb:r2dbc-mariadb (Maven). Ecosystems affected: Maven.

How do I fix CVE-2026-55859?

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.

How do I detect CVE-2026-55859 in my Maven dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.mariadb:r2dbc-mariadb, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-55859 if there is no patch (or I can't update yet)?

Until you can upgrade, make sure every query built from user input uses parameterised statements or a prepared-statement API rather than string concatenation, and reduce the database account's privileges so an injected query cannot read or alter data beyond what the feature needs.

Is CVE-2026-55859 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-55859 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-55859?

CVE-2026-55859 has an EPSS (Exploit Prediction Scoring System) score of 0.5%, placing it in the 40th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-55859?

CVE-2026-55859 is classified as CWE-116 (CWE-116), CWE-838 (CWE-838). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-55859 published, and has it been updated?

CVE-2026-55859 was published on August 28, 2026 and was last updated on September 10, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

☕

☕ Maven

Not in CISA KEV

MEDIUM severity

CVE-2026-55859 — r2dbc-mariadb

MEDIUMFix: mariadb-corporation/mariadb-connector-r2dbc@38bad9a

CVE-2026-55859 is a medium-severity (CVSS 5.9) CWE-116 vulnerability in org.mariadb:r2dbc-mariadb. A fix is available for org.mariadb:r2dbc-mariadb — see the affected versions and patch details below.

MariaDB Connector/R2DBC: Inappropriate Encoding for Output Context and Improper Encoding or Escaping of Output in org.mariadb:r2dbc-mariadb

Also known asGHSA-5rqc-86vf-g8r2

Published

Aug 28, 2026

Updated

Sep 10, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 13, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-55859.

EPSS Exploitation Probability

via FIRST.org ↗

0.5%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs40th percentile — riskier than 40% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-55859 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,987 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

☕org.mariadb:r2dbc-mariadb

Real-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

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
☕Maven	`org.mariadb:r2dbc-mariadb`	all versions	1.4.1`org.mariadb:r2dbc-mariadb:1.4.1`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.mariadb:r2dbc-mariadb, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
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
Until you can upgrade, make sure every query built from user input uses parameterised statements or a prepared-statement API rather than string concatenation, and reduce the database account's privileges so an injected query cannot read or alter data beyond what the feature needs.

Frequently Asked Questions

### 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-tra