CVE-2026-28388Network attack vector

Application crash via missing CRL number check

Published Apr 7, 2026 · Updated Apr 7, 2026

NULL pointer dereference in OpenSSL delta CRL verification allows remote attackers to crash applications with a malformed revocation list. The delta CRL processing path dereferences the required CRL Number extension without checking whether the parsed pointer is NULL. Reachability requires X509_V_FLAG_USE_DELTAS plus a freshestCRL extension or EXFLAG_FRESHEST on the base CRL; the result is a crash only.

CVSS severity7.5
High
EPSS probability0.89%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

NULL pointer dereference in OpenSSL delta CRL verification allows remote attackers to crash applications with a malformed revocation list. The delta CRL processing path dereferences the required CRL Number extension without checking whether the parsed pointer is NULL. Reachability requires X509_V_FLAG_USE_DELTAS plus a freshestCRL extension or EXFLAG_FRESHEST on the base CRL; the result is a crash only.

The record

CVE
CVE-2026-28388
Published
Apr 7, 2026
Updated
Apr 7, 2026
Vendor
OpenSSL Project
Product
OpenSSL
Classifications
CWE-476, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 7, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 7, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=1.0.2 <1.0.2zp
  2. Affected versionversion=1.1.1 <1.1.1zg
  3. Affected versionversion=3.0.0 <3.0.20
  4. Affected versionversion=3.3.0 <3.3.7
  5. Affected versionversion=3.4.0 <3.4.5
  6. Affected versionversion=3.5.0 <3.5.6
  7. Affected versionversion=3.6.0 <3.6.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

OpenSSL Project · OpenSSLversion=1.0.2 <1.0.2zp; version=1.1.1 <1.1.1zg; version=3.0.0 <3.0.20; version=3.3.0 <3.3.7; version=3.4.0 <3.4.5; version=3.5.0 <3.5.6; version=3.6.0 <3.6.2

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
7.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-476NULL Pointer Dereference
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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