OpenSSL TLS 1.3 CompressedCertificate Excessive Memory Allocation DoS
CVE-2025-66199 is a denial-of-service flaw in OpenSSL's handling of TLS 1.3 certificate compression. In affected OpenSSL 3.3, 3.4, 3.5, and 3.6 builds, when the certificate compression feature is compiled in and negotiated, the implementation uses the peer-supplied uncompressed certificate length from the TLS 1.3 CompressedCertificate message to grow a heap buffer before decompression. That length is not bounded by the configured max_cert_list certificate size limit, allowing a peer to force large allocations prior to handshake failure. The issue affects clients receiving a server CompressedCertificate and servers receiving a client CompressedCertificate in mutual TLS scenarios. The advisory states no memory corruption or information disclosure occurs.
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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
28 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
An OpenSSL vulnerability patched by upgrading to OpenSSL 3.6.1 in IPFire Core Update 200.
Unknown (listed among related OpenSSL CVEs, but not described in the content).
Low-severity OpenSSL denial-of-service condition related to TLS 1.3 certificate compression handling.
An OpenSSL vulnerability addressed in Alpine Linux stable releases 3.20.9, 3.21.6, 3.22.3, and 3.23.3.
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.