Summary
FastAPI Guard has a regex bypass
The regular expression patched to mitigate the ReDoS vulnerability by limiting the length of string fails to catch inputs that exceed this limit.
Details
In version 3.0.1, you can find a commit like the one in the link below, which was made to prevent ReDoS.
https://github.com/rennf93/fastapi-guard/commit/d9d50e8130b7b434cdc1b001b8cfd03a06729f7f
This commit mitigates the vulnerability by limiting the length of the input string, as shown in the example below.r"<script[^>]*>[^<]*<\\/script\\s*>" -> <script[^>]{0,100}>[^<]{0,1000}<\\/script\\s{0,10}>
This type of patch fails to catch cases where the string representing the attributes of a
Impact
Due to this vulnerability, most of the regex patterns can potentially be bypassed, making the application vulnerable to attacks such as XSS and SQL Injection.
The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths. Typical impact: varies by context: data corruption, logic bypass, or denial of service.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2025-54365? CVE-2025-54365 is a high-severity improper input validation vulnerability in fastapi-guard (pip), affecting versions = 3.0.1. It is fixed in 3.0.2. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.
- Which versions of fastapi-guard are affected by CVE-2025-54365? fastapi-guard (pip) versions = 3.0.1 is affected.
- Is there a fix for CVE-2025-54365? Yes. CVE-2025-54365 is fixed in 3.0.2. Upgrade to this version or later.
- Is CVE-2025-54365 exploitable, and should I be worried? Whether CVE-2025-54365 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2025-54365 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2025-54365? Upgrade
fastapi-guardto 3.0.2 or later.