block_buffer: panic corrupts inline buffer position
Affects block_bufferSource GCVE Database
CVSS 6.3 Medium : upgrade to 0.12.1 when convenient.
Data as of 30 Oct 2026, 16:33 UTC
- Patch
- Available – fixed in 0.12.1
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:NWhat to do
Upgrade block_buffer to 0.12.1.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| crates.ioblock_buffer | Affected
| Fixed in
|
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Description
### Summary A caught panic may leave the cursor position of `EagerBuffer` or `ReadBuffer` in a corrupted state; this in turn allows out-of-bounds reads/writes. ### Details & PoC The following two tests fail miri: ```rust #[cfg(miri)] #[test] fn eager_digest_blocks_panic_corrupts_inline_position() { // `EagerBuffer` stores its cursor in the last byte of the internal block. // When `digest_blocks` completes a previously partial block, it overwrites // that byte with input data before invoking the caller-provided `compress` // callback. If the callback panics, safe code can catch the panic and keep // using the buffer while its cursor byte no longer satisfies the internal // `pos < block_size` invariant. Under Miri this `get_pos` call reaches the // `unreachable_unchecked` used for the assumed-valid cursor. let mut buf = EagerBuffer::<U4>::new(&[1, 2]); let _ = std::panic::catch_unwind(std::panic::AssertUnwindSafe(|| { buf.digest_blocks(&[3, 0xff], |_| panic!("simulated compression failure")); })); let _ = buf.get_pos(); } #[cfg(miri)] #[test] fn read_buffer_generator_panic_corrupts_inline_position() { // `ReadBuffer` stores its cursor in `buffer[0]`, but `write_block` gives // `gen_block` mutable access to the whole internal block before restoring // `buffer[0]` to a valid cursor. If `gen_block` writes an arbitrary first // byte and panics, safe code can catch the panic and later observe an // invalid cursor. Under Miri this `get_pos` call reaches the // `unreachable_unchecked` used for the assumed-valid cursor. let mut buf = ReadBuffer::<U4>::default(); let _ = std::panic::catch_unwind(std::panic::AssertUnwindSafe(|| { buf.write_block( 1, |block| { block[0] = 0xff; panic!("simulated block generation failure"); }, |_| {}, ); })); let _ = buf.get_pos(); } ``` They fail on an `unreachable_unchecked!()` under the invariant for the `pos` to always be within bounds of the block. ### Impact While the byte that overwrites `pos` may come from untrusted input and is therefore attacker-controlled, this still relies on the surrounding code catching the panic and carrying on, which should be uncommon in practice. For this to be exploitable, the attacker also needs a way to trigger a panic here; I have not investigated how feasible that is. ### Credits The issue was discovered by GPT-5.5