RUSTSEC-2018-0003: Possible double free during unwinding in SmallVec::insert_many

What to do

1. See which version you have: cargo tree -i smallvec (it also shows which of your dependencies pulls it in).
2. Update within your version requirement: cargo update -p smallvec. If the fix is a newer major or minor than your requirement allows, raise it in Cargo.toml (for example smallvec = "0.6.3") or update the dependency that pulls it in.
3. Check again with cargo audit, or paste your Cargo.lock into our Cargo.toml checker.

Details from the advisory

If an iterator passed to SmallVec::insert_many panicked in Iterator::next, destructors were run during unwinding while the vector was in an inconsistent state, possibly causing a double free (a destructor running on two copies of the same value).

This is fixed in smallvec 0.6.3 by ensuring that the vector's length is not updated to include moved items until they have been removed from their original positions. Items may now be leaked if Iterator::next panics, but they will not be dropped more than once.

Thank you to @Vurich for reporting this bug.

References

• Package: crates.io/crates/smallvec
• Advisory: rustsec.org/advisories/RUSTSEC-2018-0003.html
• Report: github.com/servo/rust-smallvec/issues/96

From the RustSec Advisory Database (CC0-1.0) via the OSV export, downloaded Oct 24, 2026. Severity score computed from the published CVSS vector.

Other advisories for smallvec

• UnsoundRUSTSEC-2018-0018 · 2018-09-25smallvec creates uninitialized value of any type
• Vulnerability CriticalRUSTSEC-2019-0009 · 2019-06-06Double-free and use-after-free in SmallVec::grow()
• Vulnerability CriticalRUSTSEC-2019-0012 · 2019-07-19Memory corruption in SmallVec::grow()
• Vulnerability CriticalRUSTSEC-2021-0003 · 2021-01-08Buffer overflow in SmallVec::insert_many

Full security history of smallvec