CVE-2025-54801 is a high-severity vulnerability affecting the Fiber web framework, a popular Express-inspired framework written in Go. The vulnerability exists in versions 2.52.8 and earlier, specifically in the Ctx.BodyParser method used for parsing form data. When the form data contains a large numeric key representing a slice index (for example, test.18446744073704), the underlying schema decoder attempts to allocate a slice with length equal to the index plus one without validating whether this index is within a safe or reasonable range. This lack of validation can lead to an integer overflow or memory exhaustion, resulting in an out-of-bounds slice allocation. Consequently, the application crashes or panics due to memory allocation errors. The root cause is classified under CWE-789 (Memory Allocation with Excessive Size Value). This vulnerability does not require authentication, user interaction, or privileges to exploit, and can be triggered remotely by sending specially crafted form data to the vulnerable Fiber application. The issue was fixed in version 2.52.9 of Fiber. The CVSS v4.0 score is 8.7 (high), reflecting the vulnerability's potential to cause denial of service by crashing applications, impacting availability severely. No known exploits are currently reported in the wild, but the ease of triggering a crash remotely makes this a significant risk for affected applications.

For European organizations using Fiber versions prior to 2.52.9, this vulnerability poses a substantial risk of denial-of-service (DoS) attacks. An attacker can remotely crash web applications by sending malicious form data, leading to service outages and potential disruption of business operations. This can affect customer-facing services, internal tools, and APIs relying on Fiber, causing loss of availability and potentially damaging reputation and customer trust. In sectors such as finance, healthcare, and critical infrastructure, where uptime and service reliability are paramount, such disruptions can have severe operational and regulatory consequences. Additionally, repeated crashes could be leveraged as part of a broader attack strategy to distract or exhaust incident response resources. Although no direct data breach or code execution is indicated, the impact on availability alone is significant. European organizations with public-facing Fiber-based applications should prioritize patching to maintain service continuity and comply with regulatory requirements around operational resilience.

1. Immediate upgrade of Fiber to version 2.52.9 or later, where the vulnerability is fixed. 2. Implement input validation and rate limiting at the application or web server level to detect and block unusually large numeric keys or suspicious form data patterns before they reach the Fiber BodyParser. 3. Employ Web Application Firewalls (WAFs) with custom rules to identify and mitigate attempts to exploit this vulnerability by filtering out requests with excessively large slice indices. 4. Monitor application logs for repeated crashes or panic events related to BodyParser usage to detect potential exploitation attempts early. 5. Conduct code reviews and testing to ensure that other parts of the application do not suffer from similar unchecked memory allocations. 6. For critical systems, consider deploying runtime protection tools that can detect and prevent abnormal memory allocation patterns. 7. Educate developers and DevOps teams about this vulnerability and the importance of timely dependency updates and secure parsing practices.