CVE-2026-28388
Description
Issue summary: When a delta CRL that contains a Delta CRL Indicator extension is processed a NULL pointer dereference might happen if the required CRL Number extension is missing. Impact summary: A NULL pointer dereference can trigger a crash which leads to a Denial of Service for an application. When CRL processing and delta CRL processing is enabled during X.509 certificate verification, the delta CRL processing does not check whether the CRL Number extension is NULL before dereferencing it. When a malformed delta CRL file is being processed, this parameter can be NULL, causing a NULL pointer dereference. Exploiting this issue requires the X509_V_FLAG_USE_DELTAS flag to be enabled in the verification context, the certificate being verified to contain a freshestCRL extension or the base CRL to have the EXFLAG_FRESHEST flag set, and an attacker to provide a malformed CRL to an application that processes it. The vulnerability is limited to Denial of Service and cannot be escalated to achieve code execution or memory disclosure. For that reason the issue was assessed as Low severity according to our Security Policy. The FIPS modules in 3.6, 3.5, 3.4, 3.3 and 3.0 are not affected by this issue, as the affected code is outside the OpenSSL FIPS module boundary.
Predictions
Heuristic predictions, AS-IS, for prioritization only.
Mitigations
No mitigations published for this CVE yet.
The vendor-content worker queues fetches as references arrive (check back in a few minutes). Or — if you've already worked around this in production — publish your fix to the community-verified tier.
✚ Propose a mitigation on Community → Mitigations published via the community go through AI scoring + 2 human reviewers + 7-day silent objection window before landing here withsource_tier=community-verified.
OS impact
| OS | Version | Status | Fixed in |
|---|---|---|---|
| debian | bookworm | fixed | 3.0.19-1~deb12u2 |
| debian | bullseye | affected | |
| debian | forky | fixed | 3.6.2-1 |
| debian | sid | fixed | 3.6.2-1 |
| debian | trixie | fixed | 3.5.5-1~deb13u2 |
References
- https://github.com/openssl/openssl/commit/59c3b3158553ab53275bbbccca5cb305d591cf2e
- https://github.com/openssl/openssl/commit/5a0b4930779cd2408880979db765db919da55139
- https://github.com/openssl/openssl/commit/602542f2c0c2d5edb47128f93eac10b62aeeefb3
- https://github.com/openssl/openssl/commit/a9d187dd1000130100fa7ab915f8513532cb3bb8
- https://github.com/openssl/openssl/commit/d3a901e8d9f021f3e67d6cfbc12e768129862726
- https://openssl-library.org/news/secadv/20260407.txt
- https://cert-portal.siemens.com/productcert/html/ssa-032379.html
- https://cert-portal.siemens.com/productcert/html/ssa-265688.html
- https://security-tracker.debian.org/tracker/CVE-2026-28388
CWEs
CWE-476
Community-verified mitigations for this CVE will appear above when contributors publish them.
Verify integrity in audit chain (admin only). AS-IS.