Summary
Malicious dependencies can inject arbitrary JavaScript into cargo-generated timing reports
The Rust Security Response WG was notified that Cargo did not escape Cargo feature names when including them in the report generated by cargo build --timings. A malicious package included as a dependency may inject nearly arbitrary HTML here, potentially leading to XSS if the report is subsequently uploaded somewhere.
The severity of this vulnerability is "low" for users relying on dependencies from git, local paths, or alternative registries. Users who solely depend on crates.io are unaffected.
Note that by design Cargo allows code execution at build time, due to build scripts and procedural macros. The vulnerability in this advisory allows performing a subset of the possible damage in a harder to track down way. Your dependencies must still be trusted if you want to be protected from attacks, as it's possible to perform the same attacks with build scripts and procedural macros.
Overview
Rust 1.60.0 introduced cargo build --timings, which produces a report of how long the different steps of the build process took. It includes lists of Cargo features for each crate.
Prior to Rust 1.72, Cargo feature names were allowed to contain almost any characters (with some exceptions as used by the feature syntax), but it would produce a future incompatibility warning about them since Rust 1.49. crates.io is far more stringent about what it considers a valid feature name and has not allowed such feature names.
As the feature names defined in the Cargo.toml file were included unescaped in the timings report, they could be used to inject Javascript into the page. For example with a feature name like features = ["<img src='' onerror=alert(0)"]. If this report were subsequently uploaded to a domain that uses credentials, the injected Javascript could access resources from the website visitor.
This issue was fixed by turning the future incompatibility warning into an error.
Affected versions
The vulnerability is present in all versions of Cargo after and including 1.60.0. Rust 1.72, to be released on August 24, will include a fix for it.
Users whose dependencies are entirely on crates.io are unaffected.
Mitigations
We recommend users always excercise care in which package they download, by only including trusted dependencies in their projects. Please note that even with these vulnerabilities fixed, by design Cargo allows arbitrary code execution at build time thanks to build scripts and procedural macros: a malicious dependency will be able to cause damage regardless of these vulnerabilities.
crates.io has server-side checks preventing this attack, and there are no packages on crates.io exploiting these vulnerabilities. crates.io users still need to excercise care in choosing their dependencies though, as remote code execution is allowed by design there as well.
Impact
Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.
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-2023-40030? CVE-2023-40030 is a low-severity cross-site scripting (XSS) vulnerability in cargo (rust), affecting versions >= 1.60.0, < 1.72. It is fixed in 1.72. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
- Which versions of cargo are affected by CVE-2023-40030? cargo (rust) versions >= 1.60.0, < 1.72 is affected.
- Is there a fix for CVE-2023-40030? Yes. CVE-2023-40030 is fixed in 1.72. Upgrade to this version or later.
- Is CVE-2023-40030 exploitable, and should I be worried? Whether CVE-2023-40030 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-2023-40030 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-2023-40030? Upgrade
cargoto 1.72 or later.