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CVE-2026-78409— Util-linux: util-linux: x-mount.subdir detached-tree resolution can escape via intermediate symlinks

Quick assessment

Affected
Red Hat Red Hat Hardened Images
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.

util-linux是util-linux组织开源的一套操作系统基础工具集。 util-linux存在后置链接漏洞，该漏洞源于X-mount.subdir选项使用分离树快速路径并将配置的子目录传递给open_tree()时设置AT_SYMLINK_NOFOLLOW标志，该标志无法阻止中间符号链接遍历或将路径解析限制在新挂载的文件系统内，可能导致拥有fstab授权X-mount.subdir条目的本地非特权用户在预期挂载点附加主机路径。

CVSS 7.0 · High EPSS 0.19% · P8

Possible ATT&CK Techniques 1 AI

T1078 · Valid Accounts

Affected Version Matrix 9

VendorProduct Version RangeStatus
Red Hat Red Hat Enterprise Linux 10 any unaffected
Red Hat Red Hat Enterprise Linux 7 any unaffected
Red Hat Red Hat Enterprise Linux 8 any unaffected
Red Hat Red Hat Enterprise Linux 9 any unaffected
any unaffected
any unaffected
Red Hat Red Hat Hardened Images 2.42.2-3.4.hum1< * unaffected
Red Hat Red Hat OpenShift Container Platform 4 any unaffected
any unaffected
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I. Basic Information for CVE-2026-78409

Vulnerability Information
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Vulnerability Title
Util-linux: util-linux: x-mount.subdir detached-tree resolution can escape via intermediate symlinks
Source: CVE Program / CVE List V5
Vulnerability Description
The X-mount.subdir option uses a detached-tree fast path on Linux 6.15 and later and passes the configured subdirectory to open_tree() with AT_SYMLINK_NOFOLLOW. That flag does not stop intermediate symlink traversal or keep resolution inside the newly mounted filesystem. A local unprivileged user with an fstab-authorized X-mount.subdir entry can attach a host path at the intended mountpoint.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
在文件访问前对链接解析不恰当(链接跟随)
Source: CVE Program / CVE List V5
Vulnerability Title
util-linux 后置链接漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
util-linux是util-linux组织开源的一套操作系统基础工具集。 util-linux存在后置链接漏洞，该漏洞源于X-mount.subdir选项使用分离树快速路径并将配置的子目录传递给open_tree()时设置AT_SYMLINK_NOFOLLOW标志，该标志无法阻止中间符号链接遍历或将路径解析限制在新挂载的文件系统内，可能导致拥有fstab授权X-mount.subdir条目的本地非特权用户在预期挂载点附加主机路径。
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
Red Hat Red Hat Hardened Images 2.42.2-3.4.hum1 ~ * cpe:/a:redhat:hummingbird:1
Red Hat Red Hat Enterprise Linux 10 - cpe:/o:redhat:enterprise_linux:10
Red Hat Red Hat Enterprise Linux 7 - cpe:/o:redhat:enterprise_linux:7
Red Hat Red Hat Enterprise Linux 8 - cpe:/o:redhat:enterprise_linux:8
Red Hat Red Hat Enterprise Linux 9 - cpe:/o:redhat:enterprise_linux:9
Red Hat Red Hat Enterprise Linux 9 - cpe:/o:redhat:enterprise_linux:9
Red Hat Red Hat Enterprise Linux 9 - cpe:/o:redhat:enterprise_linux:9
Red Hat Red Hat OpenShift Container Platform 4 - cpe:/a:redhat:openshift:4
Red Hat Red Hat OpenShift Container Platform 4 - cpe:/a:redhat:openshift:4

II. Public POCs for CVE-2026-78409

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III. Intelligence Information for CVE-2026-78409

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Vendor Advisories for CVE-2026-78409 (4)

Same Patch Batch · Red Hat · 2026-09-02 · 8 CVEs total

CVE-2026-66786 9.1 CRITICAL Submariner: submariner: ipsec.conf stanza injection via remote-supplied cablename and subn
CVE-2026-78408 7.9 HIGH Util-linux: util-linux: nsenter --join-cgroup leaks root cgroup migration authority
CVE-2026-84838 7.8 HIGH Rpm: command injection in rpmuncompress via unescaped filenames passed to popen()
CVE-2026-84837 7.8 HIGH Rpm: command injection in `rpmbuild -t*` (`gettarspec`) via unescaped tarball path
CVE-2026-78410 7.8 HIGH Util-linux: util-linux: restricted bind mounts do not pin the source, allowing x-mount.own
CVE-2026-82968 6.4 MEDIUM Keycloak-services: keycloak-services: cross-session email verification proof not bound to
CVE-2026-53683 4.3 MEDIUM Freeipa: idm: idm/freeipa web ui - client-side open redirect in reset_password.html

IV. Related Vulnerabilities

Same product: Red Hat Hardened Images
Same vendor: Red Hat
Same weakness: CWE-59

V. Comments for CVE-2026-78409

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