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CVE-2026-28388 is a NULL pointer dereference vulnerability in OpenSSL's X.509 certificate verification path when processing delta certificate revocation lists (delta CRLs). The flaw occurs when a delta CRL contains a Delta CRL Indicator extension but omits the required CRL Number extension. In that condition, OpenSSL's delta CRL processing logic can dereference a NULL pointer instead of validating that the CRL Number extension is present before use. The issue is reachable during certificate verification when CRL processing and delta CRL processing are enabled. The vulnerability affects OpenSSL 3.6, 3.5, 3.4, 3.3, 3.0, 1.1.1, and 1.0.2 branches, while the OpenSSL FIPS modules for 3.6, 3.5, 3.4, 3.3, and 3.0 are not affected because the vulnerable code lies outside the FIPS module boundary.
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What an attacker gets, and what they’ve been doing with it.
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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.
16 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A specific vulnerability in OpenSSL addressed in Alpine Linux stable releases 3.20.10, 3.21.7, 3.22.4, and 3.23.4.
A NULL pointer dereference when processing a delta CRL in OpenSSL.
A NULL pointer dereference in delta CRL processing that can cause denial of service when malformed CRLs are handled.
NULL pointer dereference when processing a Delta CRL in OpenSSL.
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.