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CVE-2026-45256— Missing permission check in thr_kill2(2)

Quick assessment

Affected
FreeBSD FreeBSD
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

FreeBSD是FreeBSD基金会开源的一套类Unix操作系统。 FreeBSD存在权限许可和访问控制问题漏洞，该漏洞源于thr_kill2(2)系统调用在传递信号给特定线程时调用p_cansignal()检查权限但未检查返回值，导致即使权限检查失败信号仍被传递。此问题允许无特权的本地用户向通常无权信号的进程发送任意信号，包括其他用户或root拥有的进程以及绕过jail边界。攻击者可停止或终止任意进程（包括关键系统守护进程），造成拒绝服务。

AI Predicted 7.8 Difficulty: Moderate EPSS 0.12% · P2

Affected Version Matrix 3

VendorProduct Version RangeStatus
FreeBSD FreeBSD 15.0-RELEASE< p10 affected
14.4-RELEASE< p6 affected
14.3-RELEASE< p15 affected
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I. Basic Information for CVE-2026-45256

Vulnerability Information
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Vulnerability Title
Missing permission check in thr_kill2(2)
Source: CVE Program / CVE List V5
Vulnerability Description
When used to deliver a signal to a specific thread, thr_kill2(2) called p_cansignal() to determine whether the operation was permitted but did not check the result before delivering the signal. The signal was sent even when the permission check failed. The system call returned the resulting error to the caller, but by then the signal had already been delivered. The missing check allows an unprivileged local user who knows or can guess a target's process and thread IDs to send any signal to a process they would not normally be permitted to signal, including processes owned by other users or by root. The same check enforces jail boundaries, so a jailed process can signal processes on the host or in other jails. Thread IDs are allocated globally and sequentially, and so can be discovered by brute force with no visibility into the target. An attacker can stop or terminate arbitrary processes, including critical system daemons, resulting in a Denial of Service (DoS).
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
特权管理不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
FreeBSD 权限许可和访问控制问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
FreeBSD是FreeBSD基金会开源的一套类Unix操作系统。 FreeBSD存在权限许可和访问控制问题漏洞，该漏洞源于thr_kill2(2)系统调用在传递信号给特定线程时调用p_cansignal()检查权限但未检查返回值，导致即使权限检查失败信号仍被传递。此问题允许无特权的本地用户向通常无权信号的进程发送任意信号，包括其他用户或root拥有的进程以及绕过jail边界。攻击者可停止或终止任意进程（包括关键系统守护进程），造成拒绝服务。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
FreeBSD FreeBSD 15.0-RELEASE ~ p10 -

II. Public POCs for CVE-2026-45256

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III. Intelligence Information for CVE-2026-45256

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Vendor Advisories for CVE-2026-45256 (1)

IV. Related Vulnerabilities

Same product: FreeBSD
Same vendor: FreeBSD
Same weakness: CWE-269

V. Comments for CVE-2026-45256

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