# CVE-2026-75805: NULL Pointer Dereference in CMP Client Revocation Response Handling

Status: published. Published: 2026-09-29. Updated: 2026-11-10.

Issue summary: A CMP client that requests certificate revocation on the basis
of a PKCS#10 CSR may dereference a NULL pointer and terminate abnormally when
processing a crafted revocation response. 

Impact summary: The NULL pointer dereference happens on a read which 
leads to a crash and a Denial of Service for the affected client application.

CWE: CWE-476: NULL-pointer dereference

Description: A CMP client revoking a certificate has to tell the server which
certificate to revoke, and may do so by supplying a PKCS#10 CSR instead of the
certificate itself or its issuer name and serial number. This is
'openssl cmp -cmd rr -csr <file>' on the command line, or
OSSL_CMP_exec_RR_ses() with the certificate supplied via
OSSL_CMP_CTX_set1_p10CSR() through the API.

A CSR does not contain the issuer name and serial number of the certificate,
so the client does not send them. A server may optionally name the
certificate it revoked in its response, and the client then compares that
name against what it sent. Having sent neither an issuer name nor a serial
number, it has nothing to compare against, and a server returning a specially
crafted name causes the client to read from a NULL pointer and crash.

The revocation response is checked for valid message protection before
the affected code is reached, so an attacker must be a malicious or
compromised CMP server, or a man-in-the-middle in possession of the
secret used for message protection. Clients that identify the certificate
to be revoked by a certificate or by issuer and serial number rather
than by a PKCS#10 CSR are not affected.

FIPS impact: no
No FIPS modules are affected by this issue, as the CMP protocol
implementation is outside the OpenSSL FIPS module boundary.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: openssl) — https://github.com/openssl/openssl/commit/7ca0ccb5172a577e9b87267d77bfe21e5481a5e7
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: openssl) — https://github.com/openssl/openssl/commit/7588db7fef14209c3caa3a101d11a02006b19166
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: openssl) — https://github.com/openssl/openssl/commit/9eb2a8a9b86136cdb39d6d7d50644dd66941cdc3
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: openssl) — https://github.com/openssl/openssl/commit/abf02872a4b71767ecc72293424420f5b009190f

## Affected products and versions

- OpenSSL / OpenSSL: ≥ 4.0.0; < 4.0.3 (affected, semver); ≥ 3.6.0; < 3.6.5 (affected, semver); ≥ 3.5.0; < 3.5.9 (affected, semver); ≥ 3.4.0; < 3.4.8 (affected, semver); ≥ 3.0.0; < 3.0.23 (affected, semver). Source: CNA: openssl
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP

## Severity and prioritization

- CVSS 3.1: 5.3 (medium); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L; source: ADP: CISA-ADP

- CISA KEV: No listing in collected sources

- EPSS: 0.32% as of 2026-11-09; percentile 25.68%

- SSVC: exploitation none; automatable yes; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-476

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://openssl-library.org/news/secadv/20260929.txt (CNA: openssl; vendor-advisory)

- https://github.com/openssl/openssl/commit/7ca0ccb5172a577e9b87267d77bfe21e5481a5e7 (CNA: openssl; patch)

- https://github.com/openssl/openssl/commit/7588db7fef14209c3caa3a101d11a02006b19166 (CNA: openssl; patch)

- https://github.com/openssl/openssl/commit/9eb2a8a9b86136cdb39d6d7d50644dd66941cdc3 (CNA: openssl; patch)

- https://github.com/openssl/openssl/commit/abf02872a4b71767ecc72293424420f5b009190f (CNA: openssl; patch)

- https://cert-portal.siemens.com/productcert/html/ssa-457936.html (ADP: siemens-SADP)

## Provenance

- CNA: openssl: https://www.cve.org/CVERecord?id=CVE-2026-75805; retrieved 2026-11-10; source updated 2026-11-10

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-75805; retrieved 2026-11-10; source updated Not reported

Revision: 4efb5ffd3a247e538159bd6ff2cc2deaab51cf1999e35a372c0dcf21c9f751f2

Canonical: https://y2.dev/cve/CVE-2026-75805

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