Bug 2467064 (CVE-2026-43190)

Summary: CVE-2026-43190 kernel: netfilter: xt_tcpmss: check remaining length before reading optlen
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel, specifically within the netfilter: xt_tcpmss module. A remote attacker could exploit this vulnerability by sending a specially crafted TCP packet. The TCP option parser does not properly validate the remaining option length, which results in an out-of-bounds read. This allows an attacker to access memory beyond the intended buffer, potentially leading to information disclosure.
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Description OSIDB Bzimport 2026-05-06 13:02:19 UTC 
In the Linux kernel, the following vulnerability has been resolved:

netfilter: xt_tcpmss: check remaining length before reading optlen

Quoting reporter:
  In net/netfilter/xt_tcpmss.c (lines 53-68), the TCP option parser reads
 op[i+1] directly without validating the remaining option length.

  If the last byte of the option field is not EOL/NOP (0/1), the code attempts
  to index op[i+1]. In the case where i + 1 == optlen, this causes an
  out-of-bounds read, accessing memory past the optlen boundary
  (either reading beyond the stack buffer _opt or the
  following payload).
Comment 1 Keith Grant 2026-05-06 20:41:36 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026050642-CVE-2026-43190-f1c9@gregkh/T