CVE-2026-23398: Linux kernel · icmp: fix NULL pointer dereference in icmp_tag_validation()
Affects Linux kernelSource CVE Database V5
Not known to be exploited · fixed in d938dd5a0ad780c891ea3bc94cae7405f11e618a : update Linux kernel when convenient.
Data as of 5 Nov 2026, 22:04 UTC
Rated by Threat Radar · No CVSS score from NVD or the CNA
Thin evidence
One scorer or none- CISA SSVC
- Exploitation
- No evidence of active exploitation and no public proof of concept
- Automatable
- Attackers cannot reliably automate steps 1–4 of the kill chain
- Technical impact
- Limited control over the software or limited information exposure
CISA SSVC assessment, 2026-11-05.
- Patch
- Available – fixed in d938dd5a0ad780c891ea3bc94cae7405f11e618a, d783fa413c702ff0f8f8bea63f862e28eeaf39e3, b61529c357f1ee4d64836eb142a542d2e7ad67ce +5
Exploitation evidence
Disclosed: evidence found.
CVE published 26 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 5 Nov 2026.
What to do
Upgrade to a fixed release listed under Affected software.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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Description
In the Linux kernel, the following vulnerability has been resolved: icmp: fix NULL pointer dereference in icmp_tag_validation() icmp_tag_validation() unconditionally dereferences the result of rcu_dereference(inet_protos[proto]) without checking for NULL. The inet_protos[] array is sparse -- only about 15 of 256 protocol numbers have registered handlers. When ip_no_pmtu_disc is set to 3 (hardened PMTU mode) and the kernel receives an ICMP Fragmentation Needed error with a quoted inner IP header containing an unregistered protocol number, the NULL dereference causes a kernel panic in softirq context. Oops: general protection fault, probably for non-canonical address 0xdffffc0000000002: 0000 [#1] SMP KASAN NOPTI KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017] RIP: 0010:icmp_unreach (net/ipv4/icmp.c:1085 net/ipv4/icmp.c:1143) Call Trace: <IRQ> icmp_rcv (net/ipv4/icmp.c:1527) ip_protocol_deliver_rcu (net/ipv4/ip_input.c:207) ip_local_deliver_finish (net/ipv4/ip_input.c:242) ip_local_deliver (net/ipv4/ip_input.c:262) ip_rcv (net/ipv4/ip_input.c:573) __netif_receive_skb_one_core (net/core/dev.c:6164) process_backlog (net/core/dev.c:6628) handle_softirqs (kernel/softirq.c:561) </IRQ> Add a NULL check before accessing icmp_strict_tag_validation. If the protocol has no registered handler, return false since it cannot perform strict tag validation.
References
- git.kernel.org/stable/c/571d9d7b650f02d1e38c01128817868bceac9edd (opens in a new tab)
- git.kernel.org/stable/c/d783fa413c702ff0f8f8bea63f862e28eeaf39e3 (opens in a new tab)
- git.kernel.org/stable/c/1f9f2c6d4b2a613b7756fc5679c5116ba2ca0161 (opens in a new tab)
- git.kernel.org/stable/c/b61529c357f1ee4d64836eb142a542d2e7ad67ce (opens in a new tab)
- git.kernel.org/stable/c/9647e99d2a617c355d2b378be0ff6d0e848fd579 (opens in a new tab)
- git.kernel.org/stable/c/d938dd5a0ad780c891ea3bc94cae7405f11e618a (opens in a new tab)
- git.kernel.org/stable/c/1e4e2f5e48cec0cccaea9815fb9486c084ba41e2 (opens in a new tab)
- git.kernel.org/stable/c/614aefe56af8e13331e50220c936fc0689cf5675 (opens in a new tab)
- cert-portal.siemens.com/productcert/html/ssa-082556.html (opens in a new tab)
- cert-portal.siemens.com/productcert/html/ssa-019113.html (opens in a new tab)
- cert-portal.siemens.com/productcert/html/ssa-457936.html (opens in a new tab)
- cert-portal.siemens.com/productcert/html/ssa-784472.html (opens in a new tab)