CVE-2021-29935 is a high-severity (CVSS 7.3) Use After Free vulnerability in rocket. 1 public exploit reference exists, so weaponization risk is real. A fix is available for rocket — see the affected versions and patch details below.
Use after free in Rocket
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-29935 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,987 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
rocketReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.
Description
Affected versions of this crate transmuted a &str to a &'static str before pushing it into a StackVec, this value was then popped later in the same function.
This was assumed to be safe because the reference would be valid while the method's stack was active. In between the push and the pop, however, a function f was called that could invoke a user provided function.
If the user provided panicked, then the assumption used by the function was no longer true and the transmute to &'static would create an illegal static reference to the string. This could result in a freed string being used during (such as in a Drop implementation) or after (e.g through catch_unwind) the panic unwinding.
This flaw was corrected in commit e325e2f by using a guard object to ensure that the &'static str was dropped inside the function.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | rocket | all versions | 0.4.7cargo update -p rocket --precise 0.4.7 |
Affected Products
rocketrocketResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for rocket, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update rocket to 0.4.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-29935 is resolved across your whole dependency graph.
Workarounds
Constrain what reaches the vulnerable code: limit the size and shape of untrusted input, isolate the affected component in a sandboxed or least-privileged process, and enable the platform's memory-safety mitigations (ASLR, stack protector, hardened allocator) so an out-of-bounds access is more likely to fail closed than to be exploitable.
Frequently Asked Questions
Is CVE-2021-29935 in your dependencies?
Find it across crates.io, including transitive dependencies.