Denial of Service via crafted Ethernet frames in Cisco IOS XE for Catalyst 9000 Series Switches
CVE-2025-20311 is a denial-of-service vulnerability in Cisco IOS XE Software for Catalyst 9000 Series Switches. The flaw is caused by improper handling of certain crafted Ethernet frames. An unauthenticated adjacent attacker can exploit the issue by sending specially crafted Ethernet frames through an affected switch. If successful, the exploit causes the egress port to which the crafted frame is forwarded to become blocked and to drop all outbound traffic.
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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.
Recent activity
5 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A remote denial-of-service vulnerability affecting Cisco Catalyst 9000 devices.
A remote denial-of-service vulnerability affecting Cisco Catalyst 9000 devices.
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.