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GHSA-hppc-g8h3-xhp3

GHSA-hppc-g8h3-xhp3: rust-openssl: Unchecked callback length in PSK/cookie trampolines leaks adjacent memory to peer

The FFI trampolines behind SslContextBuilder::set_psk_client_callback, set_psk_server_callback, set_cookie_generate_cb, and set_stateless_cookie_generate_cb forwarded the user closure's returned usize directly to OpenSSL without checking it against the &mut [u8] that was handed to the closure. This can lead to buffer overflows and other unintended consequences.

(GitHub Advisory)

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GHSA-hppc-g8h3-xhp3

GHSA-hppc-g8h3-xhp3:

N/A

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
openssl	rust	>= 0.9.24, < 0.10.78	0.10.78

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability lies in several internal FFI (Foreign Function Interface) trampoline functions within the openssl::ssl::callbacks module. These functions are responsible for bridging the gap between user-provided safe Rust callbacks and the underlying C-based OpenSSL library for handling PSK (Pre-Shared Key) and DTLS cookie logic.

The root cause of the vulnerability is a failure to validate the length (usize) returned by these user callbacks. The trampolines would receive this length and pass it directly to OpenSSL. A user's callback, either maliciously or accidentally, could return a length greater than the actual size of the buffer provided for the PSK or cookie. When OpenSSL used this unchecked length, it would read past the end of the allocated buffer into adjacent memory. This out-of-bounds data could then be sent over the network to a peer, resulting in a memory leak (buffer over-read).

The patch addresses this by introducing a check in each of the four identified trampoline functions (raw_client_psk, raw_server_psk, raw_stateless_cookie_generate, raw_cookie_generate). The fix ensures that the length returned by the callback does not exceed the capacity of the buffer. If an invalid length is detected, the operation is now safely aborted instead of passing the dangerous value to OpenSSL.

Vulnerable functions

openssl::ssl::callbacks::raw_client_psk

openssl/src/ssl/callbacks.rs

This function serves as an FFI trampoline for the PSK client callback. It was vulnerable because it directly forwarded the length returned by the user-provided callback to the underlying OpenSSL library without verifying it against the allocated buffer size. This could allow a malicious callback to return a size larger than the buffer, causing OpenSSL to read adjacent memory (buffer over-read) and leak it to a network peer.

openssl::ssl::callbacks::raw_server_psk

openssl/src/ssl/callbacks.rs

This function serves as an FFI trampoline for the PSK server callback. Similar to its client counterpart, it was vulnerable because it trusted the length returned by the user callback. This allowed for a buffer over-read, where OpenSSL could read and potentially leak memory from the server's process.

openssl::ssl::callbacks::raw_stateless_cookie_generate

openssl/src/ssl/callbacks.rs

This function is the FFI trampoline for generating stateless cookies in DTLS. The vulnerability existed because the length returned from the user's cookie generation callback was not validated. An incorrect length could cause OpenSSL to read beyond the cookie buffer, leading to a memory leak in the `HelloVerifyRequest` message.

openssl::ssl::callbacks::raw_cookie_generate

openssl/src/ssl/callbacks.rs

This function is the FFI trampoline for the DTLS cookie generation callback. It was vulnerable because it did not check the length returned by the user callback against the buffer's capacity. This could lead to a buffer over-read, causing OpenSSL to use memory outside of the intended cookie buffer.

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WAF Rule

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Reasoning

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