Stream: git-wasmtime

Topic: wasmtime / issue #12592 RUSTSEC-2026-0007: Integer overfl...

Wasmtime GitHub notifications bot (Feb 14 2026 at 00:17):

github-actions[bot] opened issue #12592:

Integer overflow in BytesMut::reserve

Details
Package	bytes
Version	1.10.1
URL	https://github.com/advisories/GHSA-434x-w66g-qw3r
Date	2026-02-03
Patched versions	>=1.11.1
Unaffected versions	<1.2.1

In the unique reclaim path of BytesMut::reserve, the condition

if v_capacity >= new_cap + offset

uses an unchecked addition. When new_cap + offset overflows usize in release builds, this condition may incorrectly pass, causing self.cap to be set to a value that exceeds the actual allocated capacity. Subsequent APIs such as spare_capacity_mut() then trust this corrupted cap value and may create out-of-bounds slices, leading to UB.

This behavior is observable in release builds (integer overflow wraps), whereas debug builds panic due to overflow checks.

PoC

use bytes::*;

fn main() {
    let mut a = BytesMut::from(&b"hello world"[..]);
    let mut b = a.split_off(5);

    // Ensure b becomes the unique owner of the backing storage
    drop(a);

    // Trigger overflow in new_cap + offset inside reserve
    b.reserve(usize::MAX - 6);

    // This call relies on the corrupted cap and may cause UB & HBO
    b.put_u8(b'h');
}

Workarounds

Users of BytesMut::reserve are only affected if integer overflow checks are configured to wrap. When integer overflow is configured to panic, this issue does not apply.

See advisory page for additional details.

Wasmtime GitHub notifications bot (Feb 14 2026 at 02:29):

alexcrichton closed issue #12592:

Integer overflow in BytesMut::reserve

Details
Package	bytes
Version	1.10.1
URL	https://github.com/advisories/GHSA-434x-w66g-qw3r
Date	2026-02-03
Patched versions	>=1.11.1
Unaffected versions	<1.2.1

In the unique reclaim path of BytesMut::reserve, the condition

if v_capacity >= new_cap + offset

uses an unchecked addition. When new_cap + offset overflows usize in release builds, this condition may incorrectly pass, causing self.cap to be set to a value that exceeds the actual allocated capacity. Subsequent APIs such as spare_capacity_mut() then trust this corrupted cap value and may create out-of-bounds slices, leading to UB.

This behavior is observable in release builds (integer overflow wraps), whereas debug builds panic due to overflow checks.

PoC

use bytes::*;

fn main() {
    let mut a = BytesMut::from(&b"hello world"[..]);
    let mut b = a.split_off(5);

    // Ensure b becomes the unique owner of the backing storage
    drop(a);

    // Trigger overflow in new_cap + offset inside reserve
    b.reserve(usize::MAX - 6);

    // This call relies on the corrupted cap and may cause UB & HBO
    b.put_u8(b'h');
}

Workarounds

Users of BytesMut::reserve are only affected if integer overflow checks are configured to wrap. When integer overflow is configured to panic, this issue does not apply.

See advisory page for additional details.

Last updated: Feb 24 2026 at 04:36 UTC