{"id":"GHSA-x494-mj8g-cj27","summary":"gix-pack has multiple DoS vectors: unchecked indexing panics and uncapped OOM allocations from crafted pack data","details":"### Summary\n\nMultiple 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.\n\n### Details\n\n**Bug 1: Unchecked array indexing in delta application (CWE-248)**\n\nThe `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:\n\n```rust\npub(crate) fn apply(base: &[u8], mut target: &mut [u8], data: &[u8]) -\u003e Result\u003c(), apply::Error\u003e {\n    let mut i = 0;\n    while let Some(cmd) = data.get(i) {  // first byte: safely checked\n        i += 1;\n        match cmd {\n            cmd if cmd & 0b1000_0000 != 0 =\u003e {\n                let (mut ofs, mut size): (u32, u32) = (0, 0);\n                if cmd & 0b0000_0001 != 0 {\n                    ofs = u32::from(data[i]);     // PANIC: no bounds check\n                    i += 1;\n                }\n                // ... 6 more unchecked data[i] at lines 45, 49, 53, 57, 61, 65\n```\n\nLines 83-84 use `assert_eq!` (not `debug_assert_eq!`) that panics in both debug and release builds:\n\n```rust\n    assert_eq!(i, data.len());\n    assert_eq!(target.len(), 0);\n```\n\nA 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]`.\n\nNote: 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.\n\n**Bug 2: Uncapped allocation from attacker-controlled size headers (CWE-770)**\n\nPack 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 bound:\n\n```\nbytes_to_entries.rs:109  Vec::with_capacity(entry.decompressed_size as usize)  // UNCAPPED\nresolve.rs:461           out.resize(decompressed_len, 0)                       // UNCAPPED\nresolve.rs:190           fully_resolved_delta_bytes.resize(result_size as usize, 0)  // UNCAPPED\n```\n\nA 10-byte crafted pack entry can claim `decompressed_size = 0xFFFFFFFFFFFF` (281 TB). At `bytes_to_entries.rs:109`, gitoxide calls `Vec::with_capacity(281TB)` **before any decompression occurs**. The OS immediately OOM-kills the process. No `MAX_SIZE`, `max_object_size`, or equivalent limit exists anywhere in gix-pack.\n\nThe allocation at `resolve.rs:461` is equally dangerous: `decompressed_size` from the pack header is cast to `usize` and passed to `Vec::resize()`, which allocates and zeroes the full claimed size before the zlib decompressor runs.\n\n### PoC\n\nCompiled and executed in Rust 1.94.1 `--release` mode. All 5 panics confirmed:\n\n```\n[1] delta apply: cmd=0x81, truncated -\u003e PANIC: index out of bounds: len is 1 but index is 1\n[2] delta apply: cmd=0xFF, only 3 extra bytes -\u003e PANIC: index out of bounds: len is 4 but index is 4\n[3] parse_header_info: empty data -\u003e PANIC: index out of bounds: len is 0 but index is 0\n[4] parse_header_info: byte=0x80, truncated -\u003e PANIC: index out of bounds: len is 1 but index is 1\n[5] delta apply: assert_eq!(i, data.len()) -\u003e PANIC: assertion failed\n```\n\nFor the OOM vector: the allocation path is `parse_header_info()` -\u003e `entry.decompressed_size` (u64) -\u003e `Vec::with_capacity(size as usize)` with no intermediate validation. A minimal pack with a single entry claiming a multi-terabyte size triggers immediate process kill.\n\n### Impact\n\nAny application built on gitoxide that clones or fetches from an untrusted remote can be crashed by a malicious server:\n\n- **Panic DoS**: 1-2 bytes of crafted delta data causes an immediate process abort\n- **OOM DoS**: A single crafted pack entry header causes the process to attempt a multi-terabyte allocation, triggering an immediate OOM kill by the OS\n\nThis affects the `gix` CLI, any application using the `gix` crate, and CI/CD systems that clone repositories using gitoxide. No fuzz targets exist for gix-pack (issue #703 tracks oss-fuzz integration).\n\n### Suggested fix\n\nFor panics: replace unchecked `data[i]` with `data.get(i).ok_or(Error::...)` and replace `assert_eq!` with proper error returns.\n\nFor OOM: add a configurable maximum object size (similar to git's `transfer.maxPackSize`) and validate claimed sizes against it before allocating. At minimum, cap allocations to a reasonable default (e.g., 4 GB) and use `try_reserve()` consistently.\n\n### Severity\n\nHigh. Network vector, no privileges required, user interaction required (clone/fetch). The OOM vector is a single-packet process kill with no recovery.","aliases":["CVE-2026-82254"],"modified":"2026-08-29T03:55:59.431603308Z","published":"2026-05-05T19:24:15Z","database_specific":{"github_reviewed_at":"2026-05-05T19:24:15Z","nvd_published_at":null,"cwe_ids":["CWE-248","CWE-770"],"severity":"HIGH","github_reviewed":true},"references":[{"type":"WEB","url":"https://github.com/GitoxideLabs/gitoxide/security/advisories/GHSA-x494-mj8g-cj27"},{"type":"PACKAGE","url":"https://github.com/GitoxideLabs/gitoxide"}],"affected":[{"package":{"name":"gix-pack","ecosystem":"crates.io","purl":"pkg:cargo/gix-pack"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"0.69.0"}]}],"database_specific":{"last_known_affected_version_range":"\u003c= 0.68.0","source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/05/GHSA-x494-mj8g-cj27/GHSA-x494-mj8g-cj27.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"}]}