RUSTSEC-2021-0014: Record::read : Custom `Read` on uninitialized buffer may cause UB

What to do

1. See which version you have: cargo tree -i marc (it also shows which of your dependencies pulls it in).
2. Update within your version requirement: cargo update -p marc. If the fix is a newer major or minor than your requirement allows, raise it in Cargo.toml (for example marc = "2.0.0") 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

Affected versions of this crate passes an uninitialized buffer to a user-provided Read implementation. (Record::read())

Arbitrary Read implementations can read from the uninitialized buffer (memory exposure) and also can return incorrect number of bytes written to the buffer. Reading from uninitialized memory produces undefined values that can quickly invoke undefined behavior.

This flaw was fixed in commit 6299af0 by zero-initializing the newly allocated memory (via data.resize(len, 0)) instead of exposing uninitialized memory (unsafe { data.set_len(len) }).

References

• Package: crates.io/crates/marc
• Advisory: rustsec.org/advisories/RUSTSEC-2021-0014.html
• Report: github.com/blackbeam/rust-marc/issues/7

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