In the Linux kernel, the following vulnerability has been resolved: netfilter: nft_ct: bail out on template ct in get eval I noticed this issue while looking at a historic syzbot report [1]. A rule like the one below is enough to trigger the bug: table ip t { chain pre { type filter hook prerouting priority raw; ct zone set 1 ct original saddr 1.2.3.4 accept } } The first expression attaches a per-cpu template ct via nft_ct_set_zone_eval() (nf_ct_tmpl_alloc -> kzalloc, tuple is all zero, nf_ct_l3num(ct) == 0). The next expression then calls nft_ct_get_eval() on the same skb, treats the template as a real ct and hits the 16-byte memcpy path. With dreg at NFT_REG32_15 this overflows past struct nft_regs on the kernel stack; with smaller dreg values it silently clobbers adjacent registers. Reject template ct at the eval entry and in nft_ct_get_fast_eval(), mirroring the check nft_ct_set_eval() already has. Additionally, bound the address copy in NFT_CT_SRC / NFT_CT_DST by priv->len instead of by nf_ct_l3num(ct): nf_ct_get_tuple() zeroes the tuple before pkt_to_tuple() fills in only the protocol-relevant leading bytes, so the trailing bytes of tuple->{src,dst}.u3.all are well-defined zero. priv->len is validated at rule load, so the copy size is now bounded by the destination register rather than by an untrusted field on the conntrack. [1]: https://syzkaller.appspot.com/bug?id=389cf09cb72926114fce90dc85a2c3231dcb647c

A flaw was found in the Linux kernel's netfilter subsystem. A local attacker can exploit this vulnerability by creating specially crafted netfilter rules. This can lead to a memory corruption issue, where data on the kernel's memory stack is overwritten. Successful exploitation could result in information disclosure or potentially allow the attacker to gain elevated privileges.

nft_ct_get_eval() can treat a per CPU template conntrack object as a real conntrack entry after a rule first attaches a template ct and then reads ct original address fields from the same skb. In that state nf_ct_l3num(ct) can be 0 and the old code may take the 16 byte address copy path even when the destination register was validated for a shorter value. With dreg set near the end of struct nft_regs, this becomes an out of bounds write past the nft_regs area on the kernel stack. For the CVSS the PR:L is used because reliable triggering requires local ability to install crafted nftables rules, typically CAP_NET_ADMIN or delegated network administration in a namespace. Impact is at least local denial of service. Mitigation for this issue is either not available or the currently available options don't meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability. Red Hat Enterprise Linux 10 Fix deferred kernel Red Hat Enterprise Linux 6 Not affected kernel Red Hat Enterprise Linux 7 Fix deferred kernel Red Hat Enterprise Linux 7 Fix deferred kernel-rt Red Hat Enterprise Linux 8 Fix deferred kernel Red Hat Enterprise Linux 8 Fix deferred kernel-rt Red Hat Enterprise Linux 9 Fix deferred kernel Red Hat Enterprise Linux 9 Fix deferred kernel-rt https://www.cve.org/CVERecord?id=CVE-2026-53267 https://nvd.nist.gov/vuln/detail/CVE-2026-53267 https://lore.kernel.org/linux-cve-announce/2026062517-CVE-2026-53267-8abd@gregkh/T