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CVE Record

CVE-2025-38622: net: drop UFO packets in udp_rcv_segment()

In the Linux kernel, the following vulnerability has been resolved: net: drop UFO packets in udp_rcv_segment() When sending a packet with virtio_net_hdr to tun device, if the gso_type in virtio_net_hdr is SKB_GSO_UDP and the gso_size is less than udphdr size, below crash may happen. ------------[ cut here ]------------ kernel BUG at net/core/skbuff.c:4572! Oops: invalid opcode: 0000 [#1] SMP NOPTI CPU: 0 UID: 0 PID: 62 Comm: mytest Not tainted 6.16.0-rc7 #203 PREEMPT(voluntary) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014 RIP: 0010:skb_pull_rcsum+0x8e/0xa0 Code: 00 00 5b c3 cc cc cc cc 8b 93 88 00 00 00 f7 da e8 37 44 38 00 f7 d8 89 83 88 00 00 00 48 8b 83 c8 00 00 00 5b c3 cc cc cc cc <0f> 0b 0f 0b 66 66 2e 0f 1f 84 00 000 RSP: 0018:ffffc900001fba38 EFLAGS: 00000297 RAX: 0000000000000004 RBX: ffff8880040c1000 RCX: ffffc900001fb948 RDX: ffff888003e6d700 RSI: 0000000000000008 RDI: ffff88800411a062 RBP: ffff8880040c1000 R08: 0000000000000000 R09: 0000000000000001 R10: ffff888003606c00 R11: 0000000000000001 R12: 0000000000000000 R13: ffff888004060900 R14: ffff888004050000 R15: ffff888004060900 FS: 000000002406d3c0(0000) GS:ffff888084a19000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000020000040 CR3: 0000000004007000 CR4: 00000000000006f0 Call Trace: <TASK> udp_queue_rcv_one_skb+0x176/0x4b0 net/ipv4/udp.c:2445 udp_queue_rcv_skb+0x155/0x1f0 net/ipv4/udp.c:2475 udp_unicast_rcv_skb+0x71/0x90 net/ipv4/udp.c:2626 __udp4_lib_rcv+0x433/0xb00 net/ipv4/udp.c:2690 ip_protocol_deliver_rcu+0xa6/0x160 net/ipv4/ip_input.c:205 ip_local_deliver_finish+0x72/0x90 net/ipv4/ip_input.c:233 ip_sublist_rcv_finish+0x5f/0x70 net/ipv4/ip_input.c:579 ip_sublist_rcv+0x122/0x1b0 net/ipv4/ip_input.c:636 ip_list_rcv+0xf7/0x130 net/ipv4/ip_input.c:670 __netif_receive_skb_list_core+0x21d/0x240 net/core/dev.c:6067 netif_receive_skb_list_internal+0x186/0x2b0 net/core/dev.c:6210 napi_complete_done+0x78/0x180 net/core/dev.c:6580 tun_get_user+0xa63/0x1120 drivers/net/tun.c:1909 tun_chr_write_iter+0x65/0xb0 drivers/net/tun.c:1984 vfs_write+0x300/0x420 fs/read_write.c:593 ksys_write+0x60/0xd0 fs/read_write.c:686 do_syscall_64+0x50/0x1c0 arch/x86/entry/syscall_64.c:63 </TASK> To trigger gso segment in udp_queue_rcv_skb(), we should also set option UDP_ENCAP_ESPINUDP to enable udp_sk(sk)->encap_rcv. When the encap_rcv hook return 1 in udp_queue_rcv_one_skb(), udp_csum_pull_header() will try to pull udphdr, but the skb size has been segmented to gso size, which leads to this crash. Previous commit cf329aa42b66 ("udp: cope with UDP GRO packet misdirection") introduces segmentation in UDP receive path only for GRO, which was never intended to be used for UFO, so drop UFO packets in udp_rcv_segment().

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2025-38622 is a Linux kernel networking bug that can crash the kernel when specially formed UDP offload packets reach the TUN path. The main business risk is service disruption on affected Linux hosts, especially where untrusted workloads can interact with virtual networking. Public sources do not show active exploitation.

Executive priority

Treat as a timely kernel stability update, not an emergency internet-wide compromise. Prioritize multi-tenant Linux, virtualization, container, VPN, and network-service hosts where a crash could affect many users or critical workloads.

Technical view

The flaw is in udp_rcv_segment(). UFO packets were not intended for the UDP receive segmentation path introduced for GRO. With a virtio_net_hdr indicating UDP GSO and an invalid small gso_size, later UDP processing can hit a kernel BUG in skb_pull_rcsum, causing an oops/crash. The fix drops UFO packets in this path.

Likely exposure

Linux systems using affected kernel versions are potentially exposed. Practical exposure appears tied to access to TUN/virtual networking paths and crafted virtio_net_hdr traffic. Hosts running containers, virtualization, VPN, or network emulation should prioritize inventory. Exact impact by distribution depends on vendor kernel backports.

Exploitation context

No KEV listing or cited source confirms active exploitation. The CVE text describes a reproducible crash scenario, not privilege escalation or data theft. Exploitation likely requires a position able to send crafted traffic through a TUN device or equivalent virtual networking interface.

Researcher notes

The public record identifies the vulnerable logic and stable fix direction, but does not provide CVSS, CWE, or confirmed exploitation. Avoid assuming remote reachability without local environment evidence. Validate exposure through kernel lineage and whether TUN-based packet injection is available to untrusted contexts.

Mitigation direction

  • Apply Linux kernel updates containing the referenced stable fixes.
  • Follow distribution advisories, including Debian LTS notices where applicable.
  • Restrict untrusted access to TUN/TAP and virtual networking features.
  • Prioritize shared hosts running containers, VPNs, or virtualization networking.

Validation and detection

  • Inventory Linux kernel versions across servers, appliances, and cloud images.
  • Compare deployed kernels with vendor advisories and referenced stable commits.
  • Check whether untrusted users or workloads can access TUN/TAP networking.
  • Review crash logs for BUG/Oops traces involving skb_pull_rcsum and UDP receive paths.
Prepared
Confidence
medium
Sources
12

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

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CVE-2025-38622 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
3Timeline events
1ADP providers
12Source links

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CVECVE Program Container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxcf329aa42b6659204fee865bbce0ea20462552eb, cf329aa42b6659204fee865bbce0ea20462552eb, cf329aa42b6659204fee865bbce0ea20462552eb, cf329aa42b6659204fee865bbce0ea20462552eb, cf329aa42b6659204fee865bbce0ea20462552eb, cf329aa42b6659204fee865bbce0ea20462552eb, cf329aa42b6659204fee865bbce0ea20462552eb, cf329aa42b6659204fee865bbce0ea20462552eb, cf329aa42b6659204fee865bbce0ea20462552ebunaffected
LinuxLinux5.0, 0, 5.4.297, 5.10.241, 5.15.190, 6.1.148, 6.6.102, 6.12.42, 6.15.10, 6.16.1, 6.17affected
Weakness

CWE details

No CWE listed

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