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CVE-2026-63994— tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]()

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Linux kernel是美国Linux基金会开源的一款操作系统内核。 Linux kernel存在安全漏洞，该漏洞源于iptunnel_pmtud_build_icmp()和iptunnel_pmtud_build_icmpv6()在调用skb_cow()之前缓存ip_hdr()和ipv6_hdr()导致可能的释放后重用。

CVSS 9.8 · Critical EPSS 0.51% · P43

Possible ATT&CK Techniques 1 AI

T1203 · Exploitation for Client Execution

Affected Version Matrix 18

VendorProduct Version RangeStatus
Linux Linux 4cb47a8644cc9eb8ec81190a50e79e6530d0297f< 95b6d772bfe788331d9742d73eaa12e113b2adc4 affected
4cb47a8644cc9eb8ec81190a50e79e6530d0297f< 7254aef4d1a7e18e887af9010e2f2dc34806789b affected
4cb47a8644cc9eb8ec81190a50e79e6530d0297f< bf8b3f34c37c162357138e7c0942723b8b94fed1 affected
4cb47a8644cc9eb8ec81190a50e79e6530d0297f< 76cd9398a0470257ab765bdf5f358a2af2e17934 affected
4cb47a8644cc9eb8ec81190a50e79e6530d0297f< 50750d86a2e5266aba0c295483b3397843198b11 affected
4cb47a8644cc9eb8ec81190a50e79e6530d0297f< 6dff77899b9e9fe5d854abda3a98ad04e7229ef7 affected
4cb47a8644cc9eb8ec81190a50e79e6530d0297f< f3f204541f280a6ecb04503a0d6794d93990ca43 affected
4cb47a8644cc9eb8ec81190a50e79e6530d0297f< b4bc94353050b1fa7b702bd4c6600710dd926cff affected
… +10 more rows
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I. Basic Information for CVE-2026-63994

Vulnerability Information
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Vulnerability Title
tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]()
Source: CVE Program / CVE List V5
Vulnerability Description
In the Linux kernel, the following vulnerability has been resolved: tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]() Sashiko found that iptunnel_pmtud_build_icmp() and iptunnel_pmtud_build_icmpv6() were caching ip_hdr() and ipv6_hdr() before an skb_cow() call which can reallocate skb->head. Fix this possible UAF by initializing the local variables after the skb_cow() call. Remove skb_reset_network_header() calls which were not needed.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Linux kernel 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会开源的一款操作系统内核。 Linux kernel存在安全漏洞，该漏洞源于iptunnel_pmtud_build_icmp()和iptunnel_pmtud_build_icmpv6()在调用skb_cow()之前缓存ip_hdr()和ipv6_hdr()导致可能的释放后重用。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux 4cb47a8644cc9eb8ec81190a50e79e6530d0297f ~ 95b6d772bfe788331d9742d73eaa12e113b2adc4 -
Linux Linux 5.9 -

II. Public POCs for CVE-2026-63994

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III. Intelligence Information for CVE-2026-63994

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Patches & Fixes for CVE-2026-63994 (8)

Same Patch Batch · Linux · 2026-07-19 · 429 CVEs total

CVE-2026-63795 10.0 CRITICAL 9p: avoid putting oldfid in p9_client_walk() error path
CVE-2026-63979 9.8 CRITICAL net/handshake: hand off the pinned file reference to accept_doit
CVE-2026-53399 9.8 CRITICAL nfsd: release layout stid on setlease failure
CVE-2026-53398 9.8 CRITICAL NFSD: Fix SECINFO_NO_NAME decode error cleanup
CVE-2026-64089 9.8 CRITICAL batman-adv: tt: fix negative last_changeset_len
CVE-2026-64025 9.8 CRITICAL bpf, skmsg: fix verdict sk_data_ready racing with ktls rx
CVE-2026-64113 9.8 CRITICAL ixgbevf: fix use-after-free in VEPA multicast source pruning
CVE-2026-63924 9.8 CRITICAL ipv6: exthdrs: refresh nh pointer after ipv6_hop_jumbo()
CVE-2026-64055 9.8 CRITICAL net: ethernet: cortina: Carry over frag counter
CVE-2026-63984 9.8 CRITICAL ipv6: rpl: fix hdrlen overflow in ipv6_rpl_srh_decompress()
CVE-2026-63888 9.8 CRITICAL scsi: target: iscsi: Fix CRC overread and double-free in iscsit_handle_text_cmd()
CVE-2026-63800 9.8 CRITICAL pNFS: Fix use-after-free in pnfs_update_layout()
CVE-2026-64037 9.8 CRITICAL wifi: iwlwifi: mld: fix TSO segmentation explosion when AMSDU is disabled
CVE-2026-63887 9.8 CRITICAL scsi: target: iscsi: Bound iscsi_encode_text_output() appends to rsp_buf
CVE-2026-64136 9.8 CRITICAL smb: client: protect tc_count increment in smb2_find_smb_sess_tcon_unlocked()
CVE-2026-64056 9.8 CRITICAL net: ethernet: cortina: Make RX SKB per-port
CVE-2026-64061 9.8 CRITICAL netfs: Fix early put of sink folio in netfs_read_gaps()
CVE-2026-64125 9.8 CRITICAL net: bcmgenet: keep RBUF EEE/PM disabled
CVE-2026-64102 9.8 CRITICAL RDMA/siw: Reject MPA FPDU length underflow before signed receive math
CVE-2026-63825 9.8 CRITICAL gcov: use atomic counter updates to fix concurrent access crashes

Showing top 20 of 429 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

V. Comments for CVE-2026-63994

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