CVE-2026-55511: Yamcs vulnerable to authenticated RCE via StreamSQL aggregate-compiler column-name injection in Yamcs `executeSql`

Should you act?

Critical, preconditions apply

Severe if exploited, but exploitation needs conditions that may not apply to you. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.7%, percentile 52: FIRST’s model estimates a 0.7% chance of exploitation activity in the next 30 days, higher than 52% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
• Needs an account (high (admin)). Exposure depends on who can log in.
• Only applies if your dependency tree includes org.yamcs:yamcs-core (Maven) >= 5.13.0, <= 5.13.1, fixed in 5.13.2; org.yamcs:yamcs-core (Maven) <= 5.12.7, fixed in 5.12.8. Check your lockfile, including transitive dependencies.

What it is

Yamcs is a mission control framework. Prior to 5.12.8 and 5.13.2, Yamcs allows a user with SystemPrivilege.ControlArchiving to create a double-quoted StreamSQL column name that is interpolated into generated Java source by Expression.fillCodeInputDefVars and Expression.sanitizeName. A sum aggregate reaches yamcs-core/src/main/java/org/yamcs/yarch/streamsql/CompilableAggregateExpression.java and yamcs-core/src/main/java/org/yamcs/yarch/streamsql/funct/SumExpression.java through SelectExpression.compile, where Janino SimpleCompiler.cook compiles the injected source. POST /api/archive/{instance}:executeSql can therefore execute arbitrary Java in the Yamcs server process, exposing mission data and credentials and permitting telemetry tampering or denial of service. This issue is fixed in versions 5.12.8 and 5.13.2.

From the GitHub advisory

Overview

Yamcs compiles StreamSQL expressions to Java on the fly with the Janino SimpleCompiler (no restrictive class-loading policy or expression sandbox). When a StreamSQL aggregate such as sum(...) is applied to a column, the column's name is interpolated unescaped into the generated Java source. Because Yamcs accepts arbitrary characters in a double-quoted column identifier and applies no validation when a column is created, an authenticated user with the ControlArchiving system privilege can craft a column name that injects arbitrary Java into the compiled aggregate and achieve Remote Code Execution on the Yamcs host via POST /api/archive/{instance}:executeSql.

This is a second, independent Janino-RCE entry point sharing the root cause of CVE-2026-44632 (GHSA-524g-x36v-9wm6). The 5.13.0 / 5.12.7 fix for CVE-2026-44632 hardened only the algorithm-override path (JavaExprAlgorithmExecutionFactory, reached via MdbOverrideApi and gated by ChangeMissionDatabase). The StreamSQL expression compiler (org.yamcs.yarch.streamsql) was not addressed and remains exploitable in 5.13.0 via a different privilege (ControlArchiving).

Impact

An authenticated Yamcs user holding SystemPrivilege.ControlArchiving can cause Yamcs to compile attacker-controlled Java source through the StreamSQL aggregate expression compiler reachable from POST /api/archive/{instance}:executeSql.

Weakness type: CWE-94.

Product: org.yamcs:yamcs-core (Maven) · Assigned by: GitHub_M · Published: 2026-08-28

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: high (admin)
• User interaction: none
• Scope: changed (can affect other components)

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 poc, automatable no, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.68% probability of exploitation activity in the next 30 days; percentile 52.

Timeline

• 2026-08-28 — CVE record published by GitHub_M
• 2026-08-28 — GitHub-reviewed advisory GHSA-3g44-3m7x-cgg2 published (critical)
• 2026-09-01 — CVE record last updated

Sources and references

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

Vulnerability records

1. GitHub Advisory GHSA-3g44-3m7x-cgg2 github.com
2. CVE.org record CVE-2026-55511 cve.org
3. NVD entry CVE-2026-55511 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com
4. github.com github.com
5. github.com github.com

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