CVE-2026-42779: Apache MINA vulnerable to Deserialization of Untrusted Data (CVE-2026-41635 Incomplete Fix)

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 0.8%, percentile 55: FIRST’s model estimates a 0.8% chance of exploitation activity in the next 30 days, higher than 55% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes org.apache.mina:mina-core (Maven) >= 2.1.0, < 2.1.12, fixed in 2.1.12; org.apache.mina:mina-core (Maven) >= 2.2.0, < 2.2.7, fixed in 2.2.7. Check your lockfile, including transitive dependencies.

What it is

The fix for CVE-2026-41635 was not applied to the 2.1.X and 2.2.X branches. Here was the original issue description: Apache MINA's AbstractIoBuffer.resolveClass() contains two branches, one of them (for static classes or primitive types) does not check the class at all, bypassing the classname allowlist and allowing arbitrary code to be executed. The fix checks if the class is present in the accepted class filter before calling Class.forName(). Affected versions are Apache MINA 2.1.0

From the GitHub advisory

The fix for CVE-2026-41635 was not applied to the 2.1.X and 2.2.X branches. Here was the original issue description:

Apache MINA's AbstractIoBuffer.resolveClass() contains two branches, one of them (for static classes or primitive types) does not check the class at all, bypassing the classname allowlist and allowing arbitrary code to be executed.

The fix checks if the class is present in the accepted class filter before calling Class.forName().

Affected versions are Apache MINA 2.1.0

The problem is resolved in Apache MINA 2.1.12, and 2.2.7 by applying the classname allowlist earlier.

Weakness type: CWE-502.

Product: org.apache.mina:mina-core (Maven) · Assigned by: apache · Published: 2026-05-01

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.76% probability of exploitation activity in the next 30 days; percentile 55.

Timeline

• 2026-05-01 — CVE record published by apache
• 2026-05-01 — GitHub-reviewed advisory GHSA-vf5j-865m-mq7c published (critical)
• 2026-05-02 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vendor and project advisories, patches

1. lists.apache.org lists.apache.org

Vulnerability records

1. GitHub Advisory GHSA-vf5j-865m-mq7c github.com
2. CVE.org record CVE-2026-42779 cve.org
3. NVD entry CVE-2026-42779 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com

Critical Maven advisories · Today’s Security Digest