GHSA-J3PX-Q95C-9683

zlib-rs stack overflow during decompression with malicious input

A denial of service vulnerability was found in zlib-rs, triggered by specially constructed input. This input causes a stack overflow, resulting in the process using zlib-rs to crash.

Workarounds

Users of zlib-rs should upgrade to the latest version. Users could alternatively run zlib-rs in a separate process to prevent a stack overflow crashing the entire program. In some situations a signal handler can be used to catch a stack overflow happening.

Due to the way LLVM handles the zlib-rs codebase, tail calls were not guaranteed. This caused certain input patterns to result in a large number of stack frames being required, quickly resulting in a stack overflow. These are unlikely to occur in practice, but a dedicated attacker can construct malicious input files.

After stack overflows were found by @inahga with a fuzzer, we dove into the assembly, and found some cases where the stack grew

.LBB109_326:
    mov rdi, rbx
    call zlib_rs::inflate::State::type_do
    jmp .LBB109_311

.LBB109_311:
    lea rsp, [rbp - 40]
    pop rbx
    pop r12
    pop r13
    pop r14
    pop r15
    pop rbp
    .cfi_def_cfa rsp, 8
    ret

LLVM wants to centralize the cleanup before the return (many other blocks jump to LBB109_311), thereby invalidating a tail call to type_do. We were not able to get rid of this call without introducing one elsewhere: we just don't currently have the power to tell LLVM what we want it to do.

So, we switch back to loop+match waiting for changes to rust to make a more efficient implementation possible. Performance-wise, the damage is relatively minimal: we're just slower in cases where we already were slower than C. We are faster in cases where the relevant code is barely touched (in these cases the logic quickly moves into a hot inner loop and just spends most of its time there).

The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap. Typical impact: resource exhaustion leading to denial of service.

GHSA-J3PX-Q95C-9683 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.4.0); upgrading removes the vulnerable code path.

Kodem intelligence

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Version 0.4.0 patches the problem and is no longer vulnerable.

1. What is GHSA-J3PX-Q95C-9683? GHSA-J3PX-Q95C-9683 is a medium-severity allocation of resources without limits or throttling vulnerability in zlib-rs (rust), affecting versions <= 0.3.1. It is fixed in 0.4.0. The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap.
2. How severe is GHSA-J3PX-Q95C-9683? GHSA-J3PX-Q95C-9683 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which packages are affected by GHSA-J3PX-Q95C-9683?
   • zlib-rs (rust) (versions <= 0.3.1)
   • libz-rs-sys (rust) (versions <= 0.3.1)
   • libz-rs-sys-cdylib (rust) (versions <= 0.3.1)
4. Is there a fix for GHSA-J3PX-Q95C-9683? Yes. GHSA-J3PX-Q95C-9683 is fixed in 0.4.0. Upgrade to this version or later.
5. Is GHSA-J3PX-Q95C-9683 exploitable, and should I be worried? Whether GHSA-J3PX-Q95C-9683 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
6. What actually determines whether GHSA-J3PX-Q95C-9683 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.
7. How do I fix GHSA-J3PX-Q95C-9683?
   • Upgrade zlib-rs to 0.4.0 or later
   • Upgrade libz-rs-sys to 0.4.0 or later
   • Upgrade libz-rs-sys-cdylib to 0.4.0 or later