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CVE-2021-20322 is an observable-discrepancy side-channel flaw in Linux kernel handling of received ICMP error messages, specifically ICMP Fragmentation Needed and ICMP Redirect packets. An off-path attacker can induce and observe distinguishable behavior that reveals whether UDP ports are open, allowing rapid port discovery and undermining the entropy provided by UDP source-port randomization. Fragmented ICMP Echo Reply handling was also identified as a useful related signal. The weakness can facilitate DNS cache-poisoning attacks against software that relies on randomized UDP source ports.
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What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
What an attacker gets, and what they’ve been doing with it.
If you can’t patch tonight, do this now.
Patch, then assume compromise.
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
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.
7 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
Linux kernel DNS cache-poisoning issue involving ICMP Fragmentation Needed responses.
Linux kernel DNS cache-poisoning vulnerability based on ICMP Fragmentation Needed replies.
Linux kernel DNS cache-poisoning issue involving ICMP fragmentation-needed replies.
Linux kernel DNS cache-poisoning vulnerability based on ICMP Fragmentation Needed replies.
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.