It's also an indirect risk, but I've seen C projects reimplement things that would be a dependency in Rust, and introduce subtle (or not subtle) bugs.
Additionally, most C libraries tend to come via UNIX package managers directly, and then consumed via CMake, pkg-config or what not.
I do agree Rust dependency trees are a problem, for security, and always compiling everything from source.
https://archlinux.org/packages/extra/x86_64/apache/
They look no different than your usual Rust crate. And their full flattened dependency trees already exceeds hundreds of packages.
C/C++ libraries have much more complex build systems with many optional features shipped inside the library. Just think of curl and how many protocols it supports.
Rust's build system, however, is extremely simplistic and limited. So to have things like multiple backends for rendering, parsing, serializing etc. you have to split your library into multiple crates due to limitations Cargo impose on you. So the full equivalent of curl will be 20+ individual crates.
I think the hundreds of dependencies is overblown due to this effect. I maintain my argument. C and C++ projects are just as complex and vulnerable. CMake and fully binary distribution via Linux package managers just hide their complexity.
I have not yet looked at any C++ code base > 1 milliom lines where I did not find at least 3 copies of zlib. Often just the compression or decompression function copy and pasted into a random file. Which version? No idea. Was it patched? Likely. Is there any documentation on how to update this? Absolutely not. Was it easy to find? No, some specialists even rename the functions so that users linking to the system zlib do not get into symbol conflicts. I have heared way to often that it is so much simpler to just copy a class over from abseil, or whatever other library than to depend on it.
Sure, you do not see dependencies, the functionality those provide are still there somewhere though -- either hidden away or in the form of reimplementations. You just do not know... and what you do not know about you can not maintain.
This is no different than C++. C++ standard library made so many compromises in the name of ABI compatibility almost none of the library is actually usable for any use case. So people start to quickly add things like boost, abseil, folly, Qt, asio, imgui, doctest etc. There are millions of small libraries everywhere too!
Their CMakeLists files or conan packages also execute random commands and in the case of supply chain compromise they are as vulnerable as Rust. Actually CMake is so complicated that one can hide an exploit a bit better than build.rs.
I don't think it is a good thing either way and both toolchains should implement ways to limit execution and isolate code generation. For the packages we also need to see stronger ownership and signing guarantees. Maybe even a domain-based validation system with TXT-keys against takeovers. Allowing random people to just register and typosquat packages is not a good idea.