Veriexec bypass and arbitrary code injection in Juniper Junos OS kernel
CVE-2025-21590 is an improper isolation or compartmentalization flaw in the Juniper Networks Junos OS kernel. According to the provided content, a local attacker with high privileges and shell access can inject arbitrary code into the memory of legitimate processes on affected devices, bypassing Junos OS Veriexec protections intended to prevent unauthorized binary execution. The issue is explicitly stated to be exploitable from the shell, not from the Junos CLI. Mandiant reporting in the provided context ties the flaw to UNC3886 activity on Juniper MX routers, where the actor used the technique to inject malicious code into legitimate process memory and perform local memory patching of Junos daemons such as snmpd and mgd.
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Impact, mitigation & remediation
What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
Impact
What an attacker gets, and what they’ve been doing with it.
Mitigation
If you can’t patch tonight, do this now.
Remediation
Patch, then assume compromise.
Exploits
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
Affected products & vendors
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
Recent activity
11 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
An improper isolation flaw affecting Juniper MX routers that was exploited by UNC3886 in a notable 2025 zero-day campaign.
An arbitrary code execution vulnerability in Juniper MX Series routers.
A Junos OS vulnerability exploited to bypass Veriexec protections and enable malicious code injection into legitimate processes.
A specific vulnerability exploited by UNC3886 during RedPenguin to enable malicious code injection into legitimate process memory.
The version that knows your environment.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.