Root escalation via fermion-wrapper symlink following
Published Apr 22, 2025 · Updated Feb 26, 2026
Symlink following in Zyxel USG FLEX H uOS 1.20 through 1.31 allows local users with shell access to overwrite arbitrary files as root. The setuid-root /usr/sbin/fermion-wrapper follows attacker-controlled symbolic links in /tmp during register-status and creates writable files at the linked paths. A low-privilege shell, such as the postgres account, is required; the published exploit overwrites /etc/ld.so.preload to obtain root.
Summary
What happened
Symlink following in Zyxel USG FLEX H uOS 1.20 through 1.31 allows local users with shell access to overwrite arbitrary files as root. The setuid-root /usr/sbin/fermion-wrapper follows attacker-controlled symbolic links in /tmp during register-status and creates writable files at the linked paths. A low-privilege shell, such as the postgres account, is required; the published exploit overwrites /etc/ld.so.preload to obtain root.
The record
- CVE
- CVE-2025-1731
- Published
- Apr 22, 2025
- Updated
- Feb 26, 2026
- Vendor
- Zyxel Networks
- Product
- USG FLEX H Series uOS Firmware
- Classifications
- CWE-732, T1068
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- Apr 22, 2025CVE publishedPublication date reported by the CVE source.
- Feb 26, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=from V1.20 through V1.31
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- raptor_fermion local privilege-escalation exploitfunctional · demonstrated
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Technologies
Your stack
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Your stack
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