CVE-2024-50035 in Linux
Summary
by MITRE • 10/21/2024
In the Linux kernel, the following vulnerability has been resolved:
ppp: fix ppp_async_encode() illegal access
syzbot reported an issue in ppp_async_encode() [1]
In this case, pppoe_sendmsg() is called with a zero size. Then ppp_async_encode() is called with an empty skb.
BUG: KMSAN: uninit-value in ppp_async_encode drivers/net/ppp/ppp_async.c:545 [inline]
BUG: KMSAN: uninit-value in ppp_async_push+0xb4f/0x2660 drivers/net/ppp/ppp_async.c:675 ppp_async_encode drivers/net/ppp/ppp_async.c:545 [inline]
ppp_async_push+0xb4f/0x2660 drivers/net/ppp/ppp_async.c:675 ppp_async_send+0x130/0x1b0 drivers/net/ppp/ppp_async.c:634 ppp_channel_bridge_input drivers/net/ppp/ppp_generic.c:2280 [inline]
ppp_input+0x1f1/0xe60 drivers/net/ppp/ppp_generic.c:2304 pppoe_rcv_core+0x1d3/0x720 drivers/net/ppp/pppoe.c:379 sk_backlog_rcv+0x13b/0x420 include/net/sock.h:1113 __release_sock+0x1da/0x330 net/core/sock.c:3072 release_sock+0x6b/0x250 net/core/sock.c:3626 pppoe_sendmsg+0x2b8/0xb90 drivers/net/ppp/pppoe.c:903 sock_sendmsg_nosec net/socket.c:729 [inline]
__sock_sendmsg+0x30f/0x380 net/socket.c:744 ____sys_sendmsg+0x903/0xb60 net/socket.c:2602 ___sys_sendmsg+0x28d/0x3c0 net/socket.c:2656 __sys_sendmmsg+0x3c1/0x960 net/socket.c:2742 __do_sys_sendmmsg net/socket.c:2771 [inline]
__se_sys_sendmmsg net/socket.c:2768 [inline]
__x64_sys_sendmmsg+0xbc/0x120 net/socket.c:2768 x64_sys_call+0xb6e/0x3ba0 arch/x86/include/generated/asm/syscalls_64.h:308 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x1e0 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f
Uninit was created at: slab_post_alloc_hook mm/slub.c:4092 [inline]
slab_alloc_node mm/slub.c:4135 [inline]
kmem_cache_alloc_node_noprof+0x6bf/0xb80 mm/slub.c:4187 kmalloc_reserve+0x13d/0x4a0 net/core/skbuff.c:587 __alloc_skb+0x363/0x7b0 net/core/skbuff.c:678 alloc_skb include/linux/skbuff.h:1322 [inline]
sock_wmalloc+0xfe/0x1a0 net/core/sock.c:2732 pppoe_sendmsg+0x3a7/0xb90 drivers/net/ppp/pppoe.c:867 sock_sendmsg_nosec net/socket.c:729 [inline]
__sock_sendmsg+0x30f/0x380 net/socket.c:744 ____sys_sendmsg+0x903/0xb60 net/socket.c:2602 ___sys_sendmsg+0x28d/0x3c0 net/socket.c:2656 __sys_sendmmsg+0x3c1/0x960 net/socket.c:2742 __do_sys_sendmmsg net/socket.c:2771 [inline]
__se_sys_sendmmsg net/socket.c:2768 [inline]
__x64_sys_sendmmsg+0xbc/0x120 net/socket.c:2768 x64_sys_call+0xb6e/0x3ba0 arch/x86/include/generated/asm/syscalls_64.h:308 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x1e0 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f
CPU: 1 UID: 0 PID: 5411 Comm: syz.1.14 Not tainted 6.12.0-rc1-syzkaller-00165-g360c1f1f24c6 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
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Analysis
by VulDB Data Team • 03/22/2026
The vulnerability identified as CVE-2024-50035 resides within the Linux kernel's Point-to-Point Protocol (PPP) implementation, specifically in the ppp_async_encode() function located in drivers/net/ppp/ppp_async.c. This flaw manifests as an uninitialized value access that occurs when pppoe_sendmsg() is invoked with a zero-sized buffer, leading to the allocation of an empty socket buffer (skb) that subsequently triggers a kernel memory sanitizer (KMSAN) error. The issue is rooted in how the kernel handles PPP asynchronous encoding when processing zero-length data packets, which results in undefined behavior due to the use of uninitialized memory.
The technical exploitation pathway begins with a PPP over Ethernet (PPPoE) message transmission where the sendmsg system call is invoked with a zero-length payload. This condition causes pppoe_sendmsg() to allocate an empty skb structure, which is then passed to ppp_async_encode(). The function attempts to process this empty buffer without proper validation, leading to a read of uninitialized memory at line 545 of ppp_async.c. The call stack reveals that the execution path traverses through ppp_async_push, ppp_async_send, and eventually reaches ppp_input, which is part of the generic PPP input processing mechanism. This sequence demonstrates how a seemingly benign zero-length packet can cascade into a memory safety violation within the kernel's network subsystem.
This vulnerability presents a significant operational risk as it could potentially be exploited to achieve information disclosure or arbitrary code execution within the kernel context. The uninitialized memory read represents a classic security weakness that may expose sensitive kernel data to user-space processes or provide an attacker with information useful for further exploitation. According to CWE-457, this corresponds to the use of uninitialized variables, while the ATT&CK framework categorizes this under privilege escalation techniques through kernel vulnerabilities. The impact is particularly concerning given that PPP is commonly used in network infrastructure and mobile communications, where kernel-level exploits can compromise entire network connections.
Mitigation strategies for this vulnerability should focus on ensuring proper validation of input data before processing within kernel space. The most effective approach involves implementing bounds checking and zero-length validation within the ppp_async_encode() function to prevent processing of empty or malformed skbs. Additionally, kernel updates and patches should be deployed immediately to address this specific flaw in the PPP subsystem. System administrators should also consider implementing network monitoring to detect anomalous PPP traffic patterns that might indicate exploitation attempts. The fix should include proper initialization of memory regions and validation of packet sizes before any encoding operations are performed, aligning with secure coding practices recommended by the Linux kernel security team and industry best practices for preventing memory safety vulnerabilities.