Weakness · Medium
CWE-567: Unsynchronized Access to Shared Data in a Multithreaded Context
What it is
The product does not properly synchronize shared data, such as static variables across threads, which can lead to undefined behavior and unpredictable data changes.
- Severity (our rating)
- Medium
- Likelihood of exploit
- Not rated by MITRE
- Introduced during
- Implementation
- Exploited in the wild
- No CVE in CISA's catalog
In more detail
Within servlets, shared static variables are not protected from concurrent access, but servlets are multithreaded. This is a typical programming mistake in J2EE applications, since the multithreading is handled by the framework. When a shared variable can be influenced by an attacker, one thread could wind up modifying the variable to contain data that is not valid for a different thread that is also using the data within the variable. Note that this weakness is not unique to servlets.
What an attacker can do
- Read Application Data (Confidentiality, Integrity, Availability)
- Modify Application Data (Confidentiality, Integrity, Availability)
- DoS: Instability (Confidentiality, Integrity, Availability)
- DoS: Crash, Exit, or Restart (Confidentiality, Integrity, Availability)
How to prevent it
Implementation
- Remove the use of static variables used between servlets. If this cannot be avoided, use synchronized access for these variables.
How to find it
- Automated Static Analysis. Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)
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Start freeSource: MITRE Common Weakness Enumeration, CWE version 4.19.1. CWE is a trademark of The MITRE Corporation.