GHSA-x494-mj8g-cj27

Summary

Multiple denial-of-service vectors in gix-pack: unchecked array indexing causes panics on crafted delta data, and uncapped attacker-controlled size headers enable OOM process kills. Both are triggered by malicious pack data received during clone/fetch.

Details

Bug 1: Unchecked array indexing in delta application (CWE-248)

The apply() function in gix-pack/src/data/delta.rs (lines 33-87) reads delta instructions using unchecked data[i] indexing at 7 locations (lines 41, 45, 49, 53, 57, 61, 65). The command byte's bits indicate how many additional bytes follow, but if the delta data is truncated, the index panics:

pub(crate) fn apply(base: &[u8], mut target: &mut [u8], data: &[u8]) -> Result<(), apply::Error> {
    let mut i = 0;
    while let Some(cmd) = data.get(i) {  // first byte: safely checked
        i += 1;
        match cmd {
            cmd if cmd & 0b1000_0000 != 0 => {
                let (mut ofs, mut size): (u32, u32) = (0, 0);
                if cmd & 0b0000_0001 != 0 {
                    ofs = u32::from(data[i]);     // PANIC: no bounds check
                    i += 1;
                }
                // ... 6 more unchecked data[i] at lines 45, 49, 53, 57, 61, 65

Lines 83-84 use assert_eq! (not debug_assert_eq!) that panics in both debug and release builds:

    assert_eq!(i, data.len());
    assert_eq!(target.len(), 0);

A second location in parse_header_info() (gix-pack/src/data/entry/decode.rs:116-129) also panics on truncated input via unchecked data[0] and data[i].

Note: PR #2059 (merged 2025-06-25) fixed the explicit panic!() for command code 0. The unchecked array indexing is a distinct class that remains unfixed.

Bug 2: Uncapped allocation from attacker-controlled size headers (CWE-770)

Pack entry headers and delta headers encode object sizes as LEB128-encoded u64 values. These sizes are used to allocate buffers before validating the actual data, with no upper...