CVE-2024-49947: Vulnerability in Linux Linux

Severity: highType: vulnerabilityCVE-2024-49947

In the Linux kernel, the following vulnerability has been resolved: net: test for not too small csum_start in virtio_net_hdr_to_skb() syzbot was able to trigger this warning [1], after injecting a malicious packet through af_packet, setting skb->csum_start and thus the transport header to an incorrect value. We can at least make sure the transport header is after the end of the network header (with a estimated minimal size). [1] [ 67.873027] skb len=4096 headroom=16 headlen=14 tailroom=0 mac=(-1,-1) mac_len=0 net=(16,-6) trans=10 shinfo(txflags=0 nr_frags=1 gso(size=0 type=0 segs=0)) csum(0xa start=10 offset=0 ip_summed=3 complete_sw=0 valid=0 level=0) hash(0x0 sw=0 l4=0) proto=0x0800 pkttype=0 iif=0 priority=0x0 mark=0x0 alloc_cpu=10 vlan_all=0x0 encapsulation=0 inner(proto=0x0000, mac=0, net=0, trans=0) [ 67.877172] dev name=veth0_vlan feat=0x000061164fdd09e9 [ 67.877764] sk family=17 type=3 proto=0 [ 67.878279] skb linear: 00000000: 00 00 10 00 00 00 00 00 0f 00 00 00 08 00 [ 67.879128] skb frag: 00000000: 0e 00 07 00 00 00 28 00 08 80 1c 00 04 00 00 02 [ 67.879877] skb frag: 00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 67.880647] skb frag: 00000020: 00 00 02 00 00 00 08 00 1b 00 00 00 00 00 00 00 [ 67.881156] skb frag: 00000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 67.881753] skb frag: 00000040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 67.882173] skb frag: 00000050: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 67.882790] skb frag: 00000060: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 67.883171] skb frag: 00000070: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 67.883733] skb frag: 00000080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 67.884206] skb frag: 00000090: 00 00 00 00 00 00 00 00 00 00 69 70 76 6c 61 6e [ 67.884704] skb frag: 000000a0: 31 00 00 00 00 00 00 00 00 00 2b 00 00 00 00 00 [ 67.885139] skb frag: 000000b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 67.885677] skb frag: 000000c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 67.886042] skb frag: 000000d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 67.886408] skb frag: 000000e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 67.887020] skb frag: 000000f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 67.887384] skb frag: 00000100: 00 00 [ 67.887878] ------------[ cut here ]------------ [ 67.887908] offset (-6) >= skb_headlen() (14) [ 67.888445] WARNING: CPU: 10 PID: 2088 at net/core/dev.c:3332 skb_checksum_help (net/core/dev.c:3332 (discriminator 2)) [ 67.889353] Modules linked in: macsec macvtap macvlan hsr wireguard curve25519_x86_64 libcurve25519_generic libchacha20poly1305 chacha_x86_64 libchacha poly1305_x86_64 dummy bridge sr_mod cdrom evdev pcspkr i2c_piix4 9pnet_virtio 9p 9pnet netfs [ 67.890111] CPU: 10 UID: 0 PID: 2088 Comm: b363492833 Not tainted 6.11.0-virtme #1011 [ 67.890183] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 [ 67.890309] RIP: 0010:skb_checksum_help (net/core/dev.c:3332 (discriminator 2)) [ 67.891043] Call Trace: [ 67.891173] <TASK> [ 67.891274] ? __warn (kernel/panic.c:741) [ 67.891320] ? skb_checksum_help (net/core/dev.c:3332 (discriminator 2)) [ 67.891333] ? report_bug (lib/bug.c:180 lib/bug.c:219) [ 67.891348] ? handle_bug (arch/x86/kernel/traps.c:239) [ 67.891363] ? exc_invalid_op (arch/x86/kernel/traps.c:260 (discriminator 1)) [ 67.891372] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:621) [ 67.891388] ? skb_checksum_help (net/core/dev.c:3332 (discriminator 2)) [ 67.891399] ? skb_checksum_help (net/core/dev.c:3332 (discriminator 2)) [ 67.891416] ip_do_fragment (net/ipv4/ip_output.c:777 (discriminator 1)) [ 67.891448] ? __ip_local_out (./include/linux/skbuff.h:1146 ./include/net/l3mdev.h:196 ./include/net/l3mdev.h:213 ne ---truncated---

AI Analysis

Technical Summary

CVE-2024-49947 is a vulnerability identified in the Linux kernel's networking stack, specifically related to the handling of checksum start offsets in the virtio_net_hdr_to_skb() function. The issue arises when a malicious packet is injected through the af_packet interface, allowing an attacker to manipulate the skb->csum_start field and consequently set the transport header to an incorrect value. This malformed packet triggers a kernel warning due to an invalid offset check, where the transport header offset is less than the expected minimal size after the network header. The vulnerability was detected by syzbot, an automated kernel fuzzer, which successfully triggered a kernel warning indicative of improper validation of checksum start values. The root cause is insufficient validation ensuring that the transport header lies beyond the network header boundary, potentially leading to out-of-bounds memory access or kernel warnings. While the vulnerability does not appear to have a known exploit in the wild, the improper handling of malformed packets could be leveraged to cause kernel instability or denial of service (DoS) conditions. The vulnerability affects multiple Linux kernel versions as indicated by the affected commit hashes, and it has been publicly disclosed without an assigned CVSS score. The patch involves adding stricter checks to ensure the transport header offset is valid relative to the network header length, preventing malformed packets from causing kernel warnings or crashes.

Potential Impact

For European organizations, the impact of CVE-2024-49947 primarily revolves around potential denial of service or system instability in Linux-based environments that utilize the affected kernel versions. Since Linux is widely deployed across servers, cloud infrastructure, and embedded devices in Europe, exploitation could disrupt critical services, especially in sectors reliant on high availability such as finance, telecommunications, healthcare, and government. The vulnerability could be exploited remotely by sending specially crafted packets to affected systems, particularly those exposing network interfaces that accept raw packets via af_packet. This could lead to kernel warnings, crashes, or forced reboots, impacting service continuity and potentially causing data loss or operational downtime. Although no known exploits exist yet, the ease of triggering the issue via network packets suggests a moderate risk of DoS attacks. Confidentiality and integrity impacts appear limited as the vulnerability does not directly enable privilege escalation or arbitrary code execution. However, the availability impact could be significant for critical infrastructure and services running vulnerable Linux kernels without mitigations.

Mitigation Recommendations

European organizations should prioritize applying the official Linux kernel patches that address this vulnerability to ensure proper validation of checksum start offsets in the networking stack. In environments where immediate patching is not feasible, network-level mitigations such as filtering or blocking suspicious or malformed packets at firewalls or intrusion prevention systems can reduce exposure. Restricting access to network interfaces that allow raw packet injection (af_packet) to trusted users and processes minimizes the attack surface. Monitoring kernel logs for warnings related to skb_checksum_help or unusual network packet anomalies can provide early detection of attempted exploitation. Additionally, organizations should maintain up-to-date kernel versions and subscribe to Linux security advisories to promptly respond to emerging threats. For virtualized environments using virtio network devices, ensuring hypervisor and guest kernel updates are synchronized is critical. Finally, implementing network segmentation and least privilege principles for network access can further reduce risk.