CVE-2025-48888 is a medium-severity vulnerability affecting the Deno runtime, which is used for executing JavaScript, TypeScript, and WebAssembly code. The issue arises from incorrect authorization handling related to permission flags. Specifically, when a user runs Deno with conflicting permission flags such as `--allow-read --deny-read`, the denial flag, which should take precedence, is ignored, resulting in read permissions being granted despite the explicit denial. This behavior extends to all global unary permissions when combined similarly with allow and deny flags. The vulnerability affects Deno versions starting from 1.41.3 up to but not including 2.1.13, versions from 2.2.0 up to but not including 2.2.13, and versions from 2.3.0 up to but not including 2.3.2. The root cause is an authorization logic flaw categorized under CWE-863 (Incorrect Authorization). Although the combination of flags causing this issue is considered nonsensical and unlikely to be used in typical scenarios, it still represents a security risk because it violates the principle of least privilege by allowing permissions that should have been denied. The vulnerability has a CVSS 4.0 base score of 5.5, indicating a medium severity level, with an attack vector that is network accessible, low attack complexity, no privileges or user interaction required, and limited impact on confidentiality and integrity. No known exploits are currently reported in the wild. Users are advised to upgrade to patched versions 2.1.13, 2.2.13, or 2.3.2 to remediate the issue.

For European organizations, the impact of this vulnerability is moderate but context-dependent. Deno is increasingly adopted for server-side scripting, automation, and microservices development due to its modern runtime capabilities. If an attacker can exploit this incorrect authorization flaw, they could potentially bypass intended permission restrictions, leading to unauthorized file reads or other privileged operations. This could expose sensitive data or internal configuration files, undermining confidentiality. However, the exploit requires the attacker to invoke Deno with a specific, conflicting set of permission flags, which is an uncommon and nonsensical usage pattern, reducing the likelihood of accidental or widespread exploitation. Still, in environments where Deno scripts are run with dynamic or user-controlled flags, or in multi-tenant systems, this vulnerability could be leveraged to escalate access. The lack of required authentication or user interaction increases the theoretical risk. European organizations relying on Deno for critical infrastructure or sensitive data processing should consider this vulnerability seriously, especially in sectors like finance, government, and technology where data confidentiality and integrity are paramount.

To mitigate this vulnerability effectively, European organizations should: 1) Immediately upgrade all Deno runtimes to versions 2.1.13, 2.2.13, or 2.3.2 where the issue is patched. 2) Audit existing Deno scripts and deployment pipelines to ensure that permission flags are not set in conflicting or nonsensical combinations, particularly avoiding simultaneous use of `--allow-*` and `--deny-*` flags for the same permission. 3) Implement strict code review and deployment policies to prevent unvetted or user-supplied permission flags from being used in production environments. 4) Employ runtime monitoring and logging to detect unusual permission flag usage or unexpected file access patterns during Deno script execution. 5) Where possible, isolate Deno execution environments using containerization or sandboxing to limit the blast radius of any potential exploitation. 6) Educate developers and DevOps teams about the correct usage of Deno permission flags and the risks of improper authorization configurations. These steps go beyond generic patching advice by focusing on operational controls and secure configuration management tailored to this specific vulnerability.