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Linux Kernel CVE-2026-43407

| EUVDEUVD-2026-28713 CRITICAL
Out-of-bounds Read (CWE-125)
2026-05-08 Linux GHSA-g5m7-8jmr-xx94
Buffer Overflow Debian Linux Information Disclosure
Critical
Disputed · 9.1 NVD
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Severity by source

Sources disagree (Medium–Critical)
NVD PRIMARY
9.1 CRITICAL
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
SUSE
CRITICAL
qualitative
Red Hat
5.5 MEDIUM
qualitative

vuln.today treats the vendor’s rating as authoritative. A higher third-party CVSS (e.g. CISA-ADP) is shown for transparency but does not drive the headline severity.

CVSS VectorNVD

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
High

Lifecycle Timeline

5
Analysis Generated
May 11, 2026 - 08:34 vuln.today
CVSS changed
May 11, 2026 - 08:22 NVD
9.1 (CRITICAL)
Patch available
May 08, 2026 - 16:18 EUVD
CVE Published
May 08, 2026 - 14:21 nvd
UNKNOWN (no severity yet)
CVE Published
May 08, 2026 - 14:21 nvd
CRITICAL 9.1

DescriptionCVE.org

In the Linux kernel, the following vulnerability has been resolved:

libceph: Fix potential out-of-bounds access in ceph_handle_auth_reply()

This patch fixes an out-of-bounds access in ceph_handle_auth_reply() that can be triggered by a message of type CEPH_MSG_AUTH_REPLY. In ceph_handle_auth_reply(), the value of the payload_len field of such a message is stored in a variable of type int. A value greater than INT_MAX leads to an integer overflow and is interpreted as a negative value. This leads to decrementing the pointer address by this value and subsequently accessing it because ceph_decode_need() only checks that the memory access does not exceed the end address of the allocation.

This patch fixes the issue by changing the data type of payload_len to u32. Additionally, the data type of result_msg_len is changed to u32, as it is also a variable holding a non-negative length.

Also, an additional layer of sanity checks is introduced, ensuring that directly after reading it from the message, payload_len and result_msg_len are not greater than the overall segment length.

BUG: KASAN: slab-out-of-bounds in ceph_handle_auth_reply+0x642/0x7a0 [libceph] Read of size 4 at addr ffff88811404df14 by task kworker/20:1/262

CPU: 20 UID: 0 PID: 262 Comm: kworker/20:1 Not tainted 6.19.2 #5 PREEMPT(voluntary) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 Workqueue: ceph-msgr ceph_con_workfn [libceph] Call Trace: <TASK> dump_stack_lvl+0x76/0xa0 print_report+0xd1/0x620 ? __pfx__raw_spin_lock_irqsave+0x10/0x10 ? kasan_complete_mode_report_info+0x72/0x210 kasan_report+0xe7/0x130 ? ceph_handle_auth_reply+0x642/0x7a0 [libceph] ? ceph_handle_auth_reply+0x642/0x7a0 [libceph] __asan_report_load_n_noabort+0xf/0x20 ceph_handle_auth_reply+0x642/0x7a0 [libceph] mon_dispatch+0x973/0x23d0 [libceph] ? apparmor_socket_recvmsg+0x6b/0xa0 ? __pfx_mon_dispatch+0x10/0x10 [libceph] ? __kasan_check_write+0x14/0x30i ? mutex_unlock+0x7f/0xd0 ? __pfx_mutex_unlock+0x10/0x10 ? __pfx_do_recvmsg+0x10/0x10 [libceph] ceph_con_process_message+0x1f1/0x650 [libceph] process_message+0x1e/0x450 [libceph] ceph_con_v2_try_read+0x2e48/0x6c80 [libceph] ? __pfx_ceph_con_v2_try_read+0x10/0x10 [libceph] ? save_fpregs_to_fpstate+0xb0/0x230 ? raw_spin_rq_unlock+0x17/0xa0 ? finish_task_switch.isra.0+0x13b/0x760 ? __switch_to+0x385/0xda0 ? __kasan_check_write+0x14/0x30 ? mutex_lock+0x8d/0xe0 ? __pfx_mutex_lock+0x10/0x10 ceph_con_workfn+0x248/0x10c0 [libceph] process_one_work+0x629/0xf80 ? __kasan_check_write+0x14/0x30 worker_thread+0x87f/0x1570 ? __pfx__raw_spin_lock_irqsave+0x10/0x10 ? __pfx_try_to_wake_up+0x10/0x10 ? kasan_print_address_stack_frame+0x1f7/0x280 ? __pfx_worker_thread+0x10/0x10 kthread+0x396/0x830 ? __pfx__raw_spin_lock_irq+0x10/0x10 ? __pfx_kthread+0x10/0x10 ? __kasan_check_write+0x14/0x30 ? recalc_sigpending+0x180/0x210 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x3f7/0x610 ? __pfx_ret_from_fork+0x10/0x10 ? __switch_to+0x385/0xda0 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1a/0x30 </TASK>

[ idryomov: replace if statements with ceph_decode_need() for payload_len and result_msg_len ]

AnalysisAI

Integer overflow in Linux kernel's libceph authentication handler enables remote memory corruption and potential system crash against unpatched systems. A malicious Ceph monitor can send a specially crafted CEPH_MSG_AUTH_REPLY message with payload_len exceeding INT_MAX, causing ceph_handle_auth_reply() to underflow a pointer and trigger out-of-bounds memory access. This allows remote unauthenticated attackers to potentially read sensitive kernel memory (high confidentiality impact) or crash the kernel (high availability impact) on systems using Ceph storage. CVSS 9.1 (Critical) reflects network attack vector with no authentication or user interaction required. EPSS score of 0.02% (7th percentile) suggests low observed exploitation likelihood. Vendor patches available for all affected kernel series (5.10.253, 5.15.203, 6.1.167, 6.6.130, 6.12.78, 6.18.19, 6.19.9, 7.0), but no active exploitation confirmed via CISA KEV.

Technical ContextAI

The vulnerability exists in libceph, the Linux kernel's client library for the Ceph distributed storage system. The flaw occurs in ceph_handle_auth_reply() when processing authentication reply messages from Ceph monitors. The function stores the payload_len field from network messages in a signed 32-bit integer (int). When a malicious monitor sends a value exceeding 2,147,483,647 (INT_MAX), integer overflow causes payload_len to wrap to a large negative value. This negative offset is then used in pointer arithmetic, causing the subsequent ceph_decode_need() macro to incorrectly validate bounds and allow out-of-bounds memory access. The vulnerable code path processes CEPH_MSG_AUTH_REPLY messages during the authentication handshake with Ceph monitors. The fix changes payload_len and result_msg_len from signed int to unsigned u32, and adds explicit sanity checks comparing these values against total segment length immediately after reading from the message. This is a classic signed/unsigned integer handling error in network protocol parsing code, representing a broader class of vulnerabilities in kernel network subsystems where untrusted length fields control memory operations.

RemediationAI

Upgrade Linux kernel to patched versions: 5.10.253+ (5.10.x LTS), 5.15.203+ (5.15.x LTS), 6.1.167+ (6.1.x LTS), 6.6.130+ (6.6.x stable), 6.12.78+ (6.12.x stable), 6.18.19+ (6.18.x), 6.19.9+ (6.19.x), or 7.0+ (mainline). Upstream patches linked in NVD advisory https://nvd.nist.gov/vuln/detail/CVE-2026-43407 and kernel.org stable tree. For systems where immediate kernel upgrade is not feasible, implement network-level compensating controls: restrict Ceph monitor access to trusted networks via firewall rules (block TCP port 6789 and 3300 from untrusted sources), deploy monitors only on isolated management networks separated from untrusted clients, and enable Ceph authentication (cephx) with strong keys to prevent unauthorized monitor impersonation (note: cephx alone does not prevent exploitation if legitimate monitor is compromised). Monitor kernel logs for KASAN slab-out-of-bounds warnings in ceph_handle_auth_reply as potential exploitation indicators. If not using Ceph storage, vulnerability has no attack surface but patching eliminates latent risk from future Ceph adoption. Network isolation trades off operational flexibility (requires dedicated management network infrastructure) but provides defense-in-depth until patching completes. Cephx authentication prevents unauthorized monitor impersonation but cannot protect against compromised legitimate monitors.

Same weakness CWE-125 – Out-of-bounds Read

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Vendor StatusVendor

SUSE

Severity: Critical
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Fixed
SUSE Linux Enterprise Desktop 15 SP7 Fixed
SUSE Linux Enterprise High Availability Extension 15 SP7 Fixed
SUSE Linux Enterprise High Availability Extension 15 SP7 Fixed
SUSE Linux Enterprise High Performance Computing 15 SP7 Fixed

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CVE-2026-43407 vulnerability details – vuln.today
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