CentOS Linux 6 [TuxCare] Security Update: kernel / kernel-abi-whitelists / kernel-debug / kernel-debug-devel / etc Multiple Vulnerabilities (CENTOS6:CLSA-2026:1794218533)

high Nessus Plugin ID 381517

Synopsis

The CentOS Linux host is missing one or more security updates.

Description

The CentOS Linux 6 host has packages installed that are affected by multiple vulnerabilities as referenced in the TuxCare CENTOS6:CLSA-2026:1794218533 advisory.

- In the Linux kernel, the following vulnerability has been resolved: smb: client: clear setuid/setgid bit on write with cifsacl/modefromsid/posix extensions When a file has the setuid or setgid bit set and is written to, the VFS strips those bits and issues a setattr with ATTR_KILL_SUID/ATTR_KILL_SGID together with an ATTR_MODE carrying the already-cleared mode. Both cifs_setattr_unix() and cifs_setattr_nounix() unconditionally dropped ATTR_MODE in that case: /* skip mode change if it's just for clearing setuid/setgid */ if (attrs->ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) attrs->ia_valid &= ~ATTR_MODE;
This is fine for the default mount, where the mode is only emulated via the DOS read-only attribute and cannot represent the setuid/setgid bits anyway. However, with the cifsacl or modefromsid mount options the mode is stored on the server through an ACL (id_mode_to_cifs_acl()), with the SMB3.1.1 POSIX extensions the mode is sent to the server directly, and with the SMB1 Unix extensions (cifs_setattr_unix) the mode is sent via CIFSSMBUnixSetPathInfo(). In all those cases dropping ATTR_MODE means the cleared mode is never pushed to the server, so the setuid/setgid bit survives the write. This is a security issue:
on local filesystems the setuid bit is stripped when a file is written, but over these cifs.ko mounts the bit persists on the server, potentially allowing an unexpected privilege escalation on subsequent execution. Fix this in two places: 1. cifs_setattr_nounix(): only take the skip mode change shortcut when the mode is emulated via the DOS read-only attribute (i.e. neither cifsacl/modefromsid nor the SMB3.1.1 POSIX extensions are in effect), so that the cleared mode is propagated to the server in the ACL / POSIX cases. 2. cifs_setattr_unix(): this function is only called when Unix extensions are in effect, so the mode is always stored on the server. Remove the shortcut entirely so that the cleared mode is always pushed. (CVE-2026-89638)

- In the Linux kernel, the following vulnerability has been resolved: net: iptunnel: fix stale transport header during tunnel decapsulation Syzbot reported a crash in qdisc_pkt_len_segs_init() caused by a stale transport_header offset after tunnel decapsulation. BUG: unable to handle page fault for address:
ffffed102091a42e Oops: Oops: 0000 [#1] SMP KASAN NOPTI CPU: 0 UID: 0 PID: 340 Comm: qdisc_uaf_repro Not tainted 7.2.0-rc4-00061-g248951ddc14d #256 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 RIP: 0010:__asan_load2 <IRQ> qdisc_pkt_len_segs_init (net/core/dev.c:4145) __dev_queue_xmit (net/core/dev.c:4787) br_dev_queue_push_xmit (net/bridge/br_forward.c:53) br_handle_frame_finish (net/bridge/br_input.c:229) br_handle_frame (net/bridge/br_input.c:315) __netif_receive_skb_core.constprop.0 (net/core/dev.c:6099)
__netif_receive_skb_list_core (net/core/dev.c:6287) netif_receive_skb_list_internal (net/core/dev.c:6445) napi_complete_done (net/core/dev.c:6813) gro_cell_poll (net/core/gro_cells.c:74) __napi_poll (net/core/dev.c:7735) net_rx_action (net/core/dev.c:7798 net/core/dev.c:7955) handle_softirqs (kernel/softirq.c:622) do_softirq (kernel/softirq.c:523 kernel/softirq.c:510 ) __local_bh_enable_ip (kernel/softirq.c:450) tun_get_user (drivers/net/tun.c:1986 (discriminator 1)) tun_chr_write_iter (drivers/net/tun.c:2032) The issue is completely latent until qdisc read transport header in commit 7fb4c1967011 (net: pull headers in qdisc_pkt_len_segs_init()). The crash requires four conditions to line up: 1. The incoming packet is encapsulated and carries GSO metadata. The outer transport header offset is stored in skb->transport_header while the packet is still in the outer tunnel context. 2. The tunnel receiver strips the outer headers. skb->data is advanced to the inner frame, but skb->transport_header is left pointing to the now-removed outer L4 header, so it becomes a negative offset relative to the new data. 3. The inner frame is not delivered to the local IP stack. Instead, it is forwarded at L2 by a bridge or HSR, so ip_rcv_core() never runs and the transport header is not reset to the inner L4 offset. 4. The forwarding path calls __dev_queue_xmit(), which enters qdisc_pkt_len_segs_init(). That function computes the GSO header length from skb_transport_offset(skb).
Because the offset is negative, the unsigned cast overflows and pskb_may_pull(skb, hdr_len + sizeof(struct tcphdr)) reads past the end of the skb, triggering a KASAN fault or page fault. The issue specifically requires GSO packets (shinfo->gso_size != 0), which are processed/aggregated through gro_cells. Fix this by clearing transport_header to the ~0U sentinel in gro_cell for all tunnnel driver. GTP does not support GRO/GSO, drop the evil GSO packets in GTP directly. (CVE-2026-98401)

- In the Linux kernel, the following vulnerability has been resolved: USB: serial: fix port tear down use- after-free Some drivers for multiport devices access port driver data from completion handlers of shared URBs submitted at attach() or first open() and stopped at disconnect() or last close(), respectively. A simple NULL check before accessing the driver data makes sure that a port state container has at least been allocated, but a completion handler can still race with port tear down. Reorder the disconnect handling so that ports are not deregistered (and their driver data freed) until after all ports have been hung up and the driver disconnect() callback has run so that all I/O has been stopped. (CVE-2026-98772)

- In the Linux kernel, the following vulnerability has been resolved: smb: client: reject SetEA requests that do not fit the request buffer CIFSSMBSetEA() copies the caller's extended attribute value into the SMB request buffer without checking that it fits. The requirement is stated in the source but was never implemented: /*BB add length check to see if it would fit in negotiated SMB buffer size BB */ /* if (ea_value_len > buffer_size - 512 (enough for header)) */ if (ea_value_len) memcpy(parm_data->list.name + name_len + 1, ea_value, ea_value_len); The only bound applied on the way in is in cifs_xattr_set():
#define MAX_EA_VALUE_SIZE CIFSMaxBufSize ... if (size > MAX_EA_VALUE_SIZE) CIFSMaxBufSize is the full payload capacity of the buffer, so a value of exactly that size leaves no room for the SMB header, the TRANS2 parameter block, the fealist header and the EA name that are written ahead of it in the same object. SendReceive() already enforces the correct limit on this very length: if (in_len > CIFSMaxBufSize + MAX_CIFS_HDR_SIZE) but it is called after the copy has taken place. An unprivileged setxattr(2) on an SMB1 mount with a 250-byte name and a 16384-byte value writes 16384 bytes starting 345 bytes into a 16588-byte cifs_request object, ending 141 bytes past it: BUG: KASAN: slab-out-of-bounds in CIFSSMBSetEA+0xabc/0xde0 Write of size 16384 at addr ffff888003aa0159 by task init/68
__asan_memcpy+0x3c/0x60 CIFSSMBSetEA+0xabc/0xde0 cifs_xattr_set+0xd3a/0xff0 __vfs_setxattr+0x13e/0x1a0 The buggy address is located 345 bytes inside of allocated 16588-byte region Apply SendReceive()'s limit to the assembled request before the copy rather than after it, and widen the byte counters so the sum cannot wrap before it is tested. byte_count is also tested against U16_MAX, because it is stored in the 16-bit pSMB->ByteCount. That becomes reachable when CIFSMaxBufSize is raised at module load, where it may be set as high as 1024*127: with a 5-byte EA name and a 65521-byte value, count is exactly U16_MAX while byte_count is 65556, and cpu_to_le16() would truncate it to 20 and transmit a frame whose ByteCount does not match its length. Testing byte_count covers count as well, since byte_count is the larger of the two and count's only 16-bit consumer is written after this point. check_add_overflow() is evaluated first so that total_len is assigned before it is reported. (CVE-2026-99109)

- In the Linux kernel, the following vulnerability has been resolved: netfilter: nfnetlink_queue: hold nfnl mutex in event notifier We must serialize the release notifier and the config netlink function. A concurrent thread can issue close() which can call the release function while unrelated socket processes UNBIND request for same portid: Oops: general protection fault, [..] RIP:
0010:__instance_destroy+0x60/0x210 [nfnetlink_queue] Call Trace: nfqnl_recv_config+0x9b0/0xdc0 [nfnetlink_queue] nfnetlink_rcv_msg+0x7c2/0xeb0 ? __pfx_nfnetlink_rcv_msg+0x10/0x10 After this, parallel UNBIND and URELEASE events are impossible. This change isn't nice, but its the shortest fix given instances are not refcounted and the nfnetlink config callback drops the rcu read lock early due to need for sleeping allocations. (CVE-2026-98624)

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

Solution

Update the affected packages based on the guidance in TuxCare advisory CENTOS6:CLSA-2026:1794218533.

Plugin Details

Severity: High

ID: 381517

File Name: tuxcare_centos_6_CLSA-2026-1794218533.nasl

Version: 1.1

Type: Local

Agent: unix

Family: CentOS Local Security Checks

Published: 11/15/2026

Updated: 11/15/2026

Supported Sensors: Continuous Assessment, Nessus Agent, Nessus

Risk Information

VPR

Risk Factor: High

Score: 7.7

Percentile: 98.82

Vendor

Vendor Severity: Important

CVSS v2

Risk Factor: Medium

Base Score: 4.6

Temporal Score: 3.6

Vector: CVSS2#AV:L/AC:L/Au:N/C:P/I:P/A:P

CVSS Score Source: CVE-2021-33033

CVSS v3

Risk Factor: High

Base Score: 7.8

Temporal Score: 7

Vector: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Temporal Vector: CVSS:3.0/E:P/RL:O/RC:C

CVSS Score Source: CVE-2026-64001

Vulnerability Information

Required KB Items: Host/OS/extended-third-party, Host/local_checks_enabled, Host/CentOS/release, Host/CentOS/rpm-list

Exploit Available: true

Exploit Ease: Exploits are available

Patch Publication Date: 11/9/2026

Vulnerability Publication Date: 3/26/2021

Reference Information

CVE: CVE-2021-33033, CVE-2023-53799, CVE-2024-40959, CVE-2026-43139, CVE-2026-63898, CVE-2026-63901, CVE-2026-63902, CVE-2026-63903, CVE-2026-63913, CVE-2026-63920, CVE-2026-63947, CVE-2026-63956, CVE-2026-64001, CVE-2026-64551, CVE-2026-74598, CVE-2026-74743, CVE-2026-89596, CVE-2026-89606, CVE-2026-89638, CVE-2026-89672, CVE-2026-89783, CVE-2026-90104, CVE-2026-90207, CVE-2026-98197, CVE-2026-98262, CVE-2026-98314, CVE-2026-98401, CVE-2026-98485, CVE-2026-98624, CVE-2026-98772, CVE-2026-99109, CVE-2026-99136, CVE-2026-99152, CVE-2026-99203, CVE-2026-99212, CVE-2026-99218, CVE-2026-99224

CLSA: 2026:1794218533

Detections

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