In the Linux kernel, the following vulnerability has been resolved:
netfilter: ip6tables: mark malformed IPv6 extension headers for hotdrop
The ah, hbh and rt matches check that the fixed extension header is
present, then use the header length field to derive the advertised
extension header length for matching.
For the ah match, add the missing advertised-length check. For hbh
and rt, update the existing advertised-length checks. In all three
cases, set hotdrop to true before returning false when the advertised
extension header length exceeds the available skb data.
Returning false treats the packet as a rule mismatch. Set hotdrop to
true and drop malformed packets so they cannot bypass rules intended
to drop packets with these IPv6 extension headers.
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
CVSS Score: 9.1
AV:N - Malformed IPv6 packets reach ah/hbh/rt ip6tables match functions through netfilter PREROUTING, INPUT, and FORWARD hooks on internet-facing servers, routers, and gateways without any local access.
AC:L - An attacker reliably crafts IPv6 packets with AH, HBH, or routing extension headers whose length field exceeds available skb data; no race, timing window, or uncontrollable victim state is required.
PR:N - Exploitation requires only sending IPv6 traffic to a host with ip6tables rules using the ah, hbh, or rt matches; no authentication, local access, or CAP_NET_ADMIN is needed by the attacker.
UI:N - No victim interaction is required; exploitation is achieved solely by sending crafted network packets to a system running vulnerable ip6tables extension-header match rules.
S:U - Impact is confined to bypassing kernel netfilter policy enforcement on the affected host or gateway; it does not cross VM, container, or IOMMU security boundaries.
C:H - Bypassing DROP rules intended to block AH, HBH, or routing-header traffic can admit packets to previously firewalled services and confidential data on protected internal networks.
I:H - Malformed packets are treated as rule non-matches instead of hotdrop failures, allowing traffic administrators configured ip6tables to reject, bypassing enforced network access controls.
A:N - The flaw is a logic error in match handling that neither corrupts memory nor triggers kernel oops, panic, or hang; there is no direct availability impact from the bug itself.
| Attack Vector |
Network |
Scope |
Unchanged |
| Attack Complexity |
Low |
Confidentiality Impact |
High |
| Privileges Required |
None |
Integrity Impact |
High |
| User Interaction |
None |
Availability Impact |
None |
AV:N - Malformed IPv6 packets reach ah/hbh/rt ip6tables match functions through netfilter PREROUTING, INPUT, and FORWARD hooks on internet-facing servers, routers, and gateways without any local access.
AC:L - An attacker reliably crafts IPv6 packets with AH, HBH, or routing extension headers whose length field exceeds available skb data; no race, timing window, or uncontrollable victim state is required.
PR:N - Exploitation requires only sending IPv6 traffic to a host with ip6tables rules using the ah, hbh, or rt matches; no authentication, local access, or CAP_NET_ADMIN is needed by the attacker.
UI:N - No victim interaction is required; exploitation is achieved solely by sending crafted network packets to a system running vulnerable ip6tables extension-header match rules.
S:U - Impact is confined to bypassing kernel netfilter policy enforcement on the affected host or gateway; it does not cross VM, container, or IOMMU security boundaries.
C:H - Bypassing DROP rules intended to block AH, HBH, or routing-header traffic can admit packets to previously firewalled services and confidential data on protected internal networks.
I:H - Malformed packets are treated as rule non-matches instead of hotdrop failures, allowing traffic administrators configured ip6tables to reject, bypassing enforced network access controls.
A:N - The flaw is a logic error in match handling that neither corrupts memory nor triggers kernel oops, panic, or hang; there is no direct availability impact from the bug itself.
CVSS 3.1