CVE-2026-18725

AI_ONLY_REPORT package: iscsi-initiator-utils-6.2.1.11-0.git4b3e853.el10

Summary: Out-of-Bounds Write and Information Disclosure via Unvalidated
IPv6 Payload Length: crafted ICMPv6 Echo Requests can cause iscsiuio to
trust an inflated ipv6_plen larger than the actual received payload,
leading to MTU-bounded out-of-bounds reads and a potential one-byte
out-of-bounds write that may disclose data beyond the valid packet boundary. Requirements to exploit: Adjacent-network access on the same L2 segment as
a system running iscsiuio on an interface that processes IPv6/NDP
traffic, plus the ability to send a crafted ICMPv6 Echo Request with a
forged IPv6.plen. No authentication or user interaction is required. Component affected: iscsi-initiator-utils (iscsiuio):
iscsiuio/src/uip/ipv6.c in ipv6_icmp_handle_echo_request() and
ipv6_insert_protocol_chksum(). Version affected: iscsi-initiator-utils-6.2.1.11-0.git4b3e853.el10 when
iscsiuio is processing IPv6/NDP traffic on a reachable interface. Patch available: no released package fix established; proposed patch
included below Version fixed: unknown Upstream coordination: Not notified. CVSS: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L - 6.3 (MEDIUM) AV:A - Reachability is limited to an attacker on the same L2 segment who
can send crafted IPv6/ICMPv6 traffic to the affected interface. AC:L - The attack relies on forging IPv6.plen; no race or unusual
environment is needed beyond the vulnerable deployment. PR:N - No privileges are required. UI:N - No user interaction is required. S:U - The impact remains within the iscsiuio process and its packet
buffer handling. C:L - The reply/checksum path can read and potentially transmit data
beyond the valid packet boundary, but the demonstrated exposure is
MTU-bounded. I:L - For odd forged lengths, the checksum path can write a single
padding byte past the valid protocol data, which may affect adjacent buffer
contents. A:L - Invalid memory access may destabilize or crash the process, but
reliable high-impact denial of service is not established from the
available evidence. Impact: Moderate. Under Red Hat's severity guidance, this is more
consistent with a flaw that can affect confidentiality, integrity, or
availability under constrained circumstances than with an Important issue.
The bug is unauthenticated and adjacent-network reachable, but the
currently supported outcome is MTU-bounded out-of-bounds access in a
deployment-dependent IPv6/NDP path, not easy remote system compromise or
clearly high-impact memory corruption. Embargo: no Reason: The currently supported impact is Moderate, exposure depends on
iscsiuio processing IPv6 traffic on a reachable L2 segment, and operators
can reduce exposure operationally by isolating or disabling the affected
path. Acknowledgement: Aisle Research Vulnerability Details: In the ICMPv6 echo-reply path, the code reuses the
inbound ipv6_plen field when sizing the reply instead of clamping it to
the bytes actually received:

/* iscsiuio/src/uip/ipv6.c */
static void ipv6_icmp_handle_echo_request(struct ipv6_context *context)
{
...
ipv6_send(context, (u8_t *) icmp - (u8_t *) eth +
sizeof(struct ipv6_hdr) + HOST_TO_NET16(ipv6->ipv6_plen));
}

Later, checksum generation also trusts ipv6_plen for memory traversal,
and for odd lengths it writes a padding byte at ptr + protocol_data_len
before iterating over protocol_data_len bytes:

/* iscsiuio/src/uip/ipv6.c */
protocol_data_len = HOST_TO_NET16(ipv6->ipv6_plen);
...
if (protocol_data_len & 1) {
*((u8_t *) ptr + protocol_data_len) = 0;
protocol_data_len++;
}
for (i = 0; i < protocol_data_len / 2; i++) {
sum += HOST_TO_NET16(*ptr);
ptr++;
}

The available receive-side logic does not establish a payload-length bound
strong enough to eliminate this condition. uip_input() compares the IPv6
payload length against uip_len, but uip_len is treated as full frame
length in the observed path rather than the actual IPv6 payload length, and
ipv6_rx_packet() receives a len argument without using it to bound
parsing. A forged ipv6_plen can therefore exceed the real IPv6 payload
stored in the buffer. The available evidence supports MTU-bounded
out-of-bounds access in normal receive paths rather than the earlier
arbitrary 64KB worst case. The affected logic appears to be present in the
available 6.2.1.11 code base, but this report is scoped to the scanned SRPM
package. Steps to reproduce:

1. Build iscsiuio with ASAN enabled.
2. Run iscsiuio with IPv6/NDP active on a test interface.
3. From the same L2 segment, send an ICMPv6 Echo Request with IPv6.plen
   set larger than the actual payload bytes in the frame buffer; one tested
   shape is plen=1491 with an Ethernet frame size near 1500 bytes.
4. Observe the reply path: ASAN reports invalid access in
   ipv6_insert_protocol_chksum() as the checksum walk reads past valid
   packet data, odd lengths may also trigger a one-byte write, and reply
   sizing is derived from the forged ipv6_plen rather than the actual
   received payload size. Mitigation: Until a fix is available, keep iscsiuio-managed interfaces on
   trusted L2 segments only. Where operationally acceptable, disable IPv6 on
   those interfaces or filter ICMPv6 Echo Requests before they reach
   iscsiuio. If iscsiuio is not processing IPv6/NDP traffic, this specific
   path is not reachable. Proposed Fix: Clamp the reply payload length to the actual received payload
   derived from context->ustack->uip_len, reject packets too short to
   contain a complete ICMPv6 header, and rewrite ipv6->ipv6_plen before
   calling ipv6_send().

diff --git a/iscsiuio/src/uip/ipv6.c b/iscsiuio/src/uip/ipv6.c
@@ -1100,6 +1100,8 @@ static void ipv6_icmp_handle_echo_request(struct  
ipv6_context *context)
{
struct eth_hdr *eth =
(struct eth_hdr *)context->ustack->data_link_layer;
+	u16_t rx_total, rx_payload, hdr_plen, safe_plen;
+	u16_t l2_l3_len = sizeof(struct eth_hdr) + sizeof(struct ipv6_hdr);
struct ipv6_hdr *ipv6 =
(struct ipv6_hdr *)context->ustack->network_layer;
struct icmpv6_hdr *icmp = (struct icmpv6_hdr *)((u8_t *)ipv6 +
@@ -1126,8 +1128,20 @@ static void ipv6_icmp_handle_echo_request(struct  
ipv6_context *context)
icmp->icmpv6_code = 0;
icmp->icmpv6_cksum = 0;
ILOG_DEBUG("IPv6: Send echo reply");
-	ipv6_send(context, (u8_t *) icmp - (u8_t *) eth +
sizeof(struct ipv6_hdr) + HOST_TO_NET16(ipv6>ipv6_plen));
+
+	rx_total = context->ustack->uip_len;
+	if (rx_total <= l2_l3_len)
+		return;
+
+	rx_payload = rx_total - l2_l3_len;
+	hdr_plen = HOST_TO_NET16(ipv6->ipv6_plen);
+	safe_plen = (hdr_plen <= rx_payload) ? hdr_plen : rx_payload;
+	if (safe_plen < sizeof(struct icmpv6_hdr))
+		return;
+
+	ipv6->ipv6_plen = HOST_TO_NET16(safe_plen);
+	ipv6_send(context, l2_l3_len + safe_plen);
+
return;
}

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