Summary
Use after free in nano_arena
Affected versions of this crate assumed that Borrow was guaranteed to return the same value on .borrow(). The borrowed index value was used to retrieve a mutable reference to a value.
If the Borrow implementation returned a different index, the split arena would allow retrieving the index as a mutable reference creating two mutable references to the same element. This violates Rust's aliasing rules and allows for memory safety issues such as writing out of bounds and use-after-frees.
The flaw was corrected in commit 6b83f9d by storing the .borrow() value in a temporary variable.
Impact
Memory is accessed after it has been freed, leading to undefined behavior in native code. Typical impact: memory corruption, crash, or potential code execution.
CVE-2021-28032 has a CVSS score of 9.8 (Critical). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.5.2); upgrading removes the vulnerable code path.
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-2021-28032? CVE-2021-28032 is a critical-severity use after free vulnerability in nano_arena (rust), affecting versions < 0.5.2. It is fixed in 0.5.2. Memory is accessed after it has been freed, leading to undefined behavior in native code.
- How severe is CVE-2021-28032? CVE-2021-28032 has a CVSS score of 9.8 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of nano_arena are affected by CVE-2021-28032? nano_arena (rust) versions < 0.5.2 is affected.
- Is there a fix for CVE-2021-28032? Yes. CVE-2021-28032 is fixed in 0.5.2. Upgrade to this version or later.
- Is CVE-2021-28032 exploitable, and should I be worried? Whether CVE-2021-28032 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-2021-28032 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-2021-28032? Upgrade
nano_arenato 0.5.2 or later.