CVE-2026-91487 in Java SE
Summary
by MITRE • 10/21/2026
Vulnerability in Oracle Java SE (component: Compiler). Supported versions that are affected are Oracle Java SE: 8u503-perf, 11.0.32.1, 17.0.20.1, 21.0.12.1, 25.0.4.1, 27; Oracle GraalVM for JDK: 17.0.20.1 and 21.0.12.1; Oracle GraalVM Enterprise Edition: 21.3.19.1.1. Difficult to exploit vulnerability allows unauthenticated attacker with network access via multiple protocols to compromise Oracle Java SE. Successful attacks of this vulnerability can result in unauthorized update, insert or delete access to some of Oracle Java SE accessible data as well as unauthorized read access to a subset of Oracle Java SE accessible data. Note: This vulnerability can only be exploited by supplying data to APIs in the specified Component without using Untrusted Java Web Start applications or Untrusted Java applets, such as through a web service. CVSS 3.1 Base Score 4.8 (Confidentiality and Integrity impacts). CVSS Vector: (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N).
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Analysis
by VulDB Data Team • 10/21/2026
The identified vulnerability resides within the Compiler component of Oracle Java SE, affecting a broad range of supported releases including version 8u503-perf and subsequent long-term support versions such as 11.0.32.1, 17.0.20.1, 21.0.12.1, 25.0.4.1, and 27. The scope of impact extends to Oracle GraalVM for JDK versions 17.0.20.1 and 21.0.12.1, as well as Oracle GraalVM Enterprise Edition version 21.3.19.1.1. This flaw represents a significant security concern because it allows an unauthenticated attacker with network access via multiple protocols to compromise the integrity of the Java SE environment. The difficulty associated with exploiting this vulnerability is classified as high, indicating that while the attack vector exists, successful exploitation requires specific conditions and precise execution rather than being trivially achievable by automated tools or casual attackers.
The technical nature of this flaw centers on improper handling of data supplied to APIs within the specified Compiler component. Unlike many Java vulnerabilities that are triggered through untrusted applets or Web Start applications which benefit from sandboxing protections, this vulnerability can be exploited directly through API calls without relying on those legacy execution contexts. This distinction is critical because it removes a common layer of defense assumed by developers who might believe their application is safe simply because it does not use Java Applets or Untrusted Java Web Start features. The attacker must supply maliciously crafted data to these APIs, which then triggers the flaw within the compiler logic itself rather than at runtime in the virtual machine execution engine. This suggests a potential issue with how source code or bytecode representations are processed during compilation phases, potentially allowing for injection of unauthorized operations into the compiled output.
The operational impact of this vulnerability is characterized by both confidentiality and integrity breaches, as reflected in its CVSS 3.1 base score of 4.8. A successful exploitation does not result in a complete system compromise or denial of service but rather enables unauthorized access to data accessible by Oracle Java SE. Specifically, the attacker gains the ability to perform unauthorized updates, inserts, or deletes against certain datasets managed by the application. Simultaneously, they achieve unauthorized read access to a subset of this same data pool. This dual impact on integrity and confidentiality means that sensitive information can be exfiltrated while also being altered, potentially leading to data corruption, financial loss, or regulatory non-compliance depending on the nature of the affected data. The attack vector is network-based with no requirement for user interaction, making it particularly dangerous in server-side environments where services are continuously exposed to external inputs.
From a classification perspective, this vulnerability aligns with CWE-787 Out-of-bounds Write or similar memory safety issues if the flaw involves buffer manipulation during compilation, though given the API context, it may also relate to CWE-94 Improper Control of Generation of Code (Code Injection) if the compiler is tricked into generating malicious bytecode. In terms of MITRE ATT&CK mapping, this behavior corresponds to techniques involving code execution or data exfiltration through legitimate system processes. The lack of authentication requirement places it under Initial Access vectors that do not require prior credentials, while the network access vector indicates remote exploitability without physical proximity.
Mitigation strategies must focus on immediate patching and architectural review. Organizations running any of the affected versions should apply the latest security patches provided by Oracle to update the Compiler component to a fixed version. Since exploitation requires supplying data to specific APIs, developers conducting code reviews should audit all entry points where external or semi-trusted data is passed into Java SE compiler APIs. Input validation and sanitization mechanisms must be strengthened at these boundaries to ensure that only expected formats are processed. Additionally, implementing strict network access controls can limit the attack surface by restricting which hosts can communicate with services utilizing vulnerable API endpoints. Monitoring for anomalous patterns in compilation requests or unexpected data modifications within application databases will aid in early detection of attempted exploits.