CVE-2025-69420: 
OpenSSL vulnerability analysis and mitigation

CVE-2025-69420 is a type confusion vulnerability in OpenSSL's TimeStamp Response (TSR) verification code that can cause a Denial of Service via NULL or invalid pointer dereference. It affects OpenSSL versions 1.1.1 (before 1.1.1ze), 3.0.0–3.0.18, 3.3.0–3.3.5, 3.4.0–3.4.3, 3.5.0–3.5.4, and 3.6.0; OpenSSL 1.0.2 is not affected. The vulnerability was disclosed on January 27, 2026, and carries a CVSS v3.1 base score of 7.5 (High) (OpenSSL Advisory, Red Hat CVE).

The root cause is a type confusion flaw (CWE-843) combined with improper validation of exceptional conditions (CWE-754) in crypto/ts/ts_rsp_verify.c. The functions ossl_ess_get_signing_cert() and ossl_ess_get_signing_cert_v2() retrieve a signing certificate attribute from a PKCS7 signer info structure and immediately access attr->value.sequence without first verifying that attr->type == V_ASN1_SEQUENCE. When a malformed TimeStamp Response contains an attribute with a non-SEQUENCE ASN.1 type, the code accesses the wrong union member, resulting in an invalid or NULL pointer dereference and a process crash. The fix, applied across all affected branches, adds a single type-check condition (attr->type != V_ASN1_SEQUENCE) before dereferencing the union member (OpenSSL Commit, OpenSSL Commit). Exploitation requires an attacker to supply a crafted TSR to an application that calls TS_RESP_verify_response(); no authentication is required, but the target application must actively use RFC 3161 timestamp verification.

Successful exploitation causes the affected application to crash, resulting in a Denial of Service with high availability impact and no confidentiality or integrity impact. The scope is limited to applications that invoke OpenSSL's TS_RESP_verify_response() function with attacker-controlled input, such as code-signing verification pipelines, PKI infrastructure, or document signing services. Because the TimeStamp protocol (RFC 3161) is not widely deployed, the practical attack surface is relatively narrow, and OpenSSL itself assessed the severity as Low despite the CVSS network-reachable score (OpenSSL Advisory). FIPS modules in versions 3.0, 3.3, 3.4, and 3.5 are not affected, as the TSR implementation lies outside the FIPS module boundary.

1. Identify a target application: Locate a service or application that uses OpenSSL's TS_RESP_verify_response() function to validate RFC 3161 TimeStamp Responses (e.g., code-signing verification tools, document signing services, or PKI validation endpoints).
2. Craft a malformed TimeStamp Response: Construct a DER-encoded TimeStamp Response (per RFC 3161) in which the signingCertificate or signingCertificateV2 signed attribute is present but its ASN.1 type is set to a non-SEQUENCE value (e.g., V_ASN1_INTEGER or V_ASN1_OCTET_STRING) instead of the expected V_ASN1_SEQUENCE.
3. Submit the malformed response: Deliver the crafted TSR to the target application through whatever channel it accepts timestamp responses — this could be a network API, a file upload interface, or a direct function call if the attacker can influence the input.
4. Trigger the crash: When the application calls ossl_ess_get_signing_cert() or ossl_ess_get_signing_cert_v2(), it accesses attr->value.sequence without validating the type, causing a NULL or invalid pointer dereference and crashing the process, achieving Denial of Service (OpenSSL Commit, OpenSSL Advisory).

• Logs: Application crash logs or core dumps originating from the OpenSSL library, specifically within ts_rsp_verify.c or functions named ossl_ess_get_signing_cert / ossl_ess_get_signing_cert_v2; segmentation fault signals (SIGSEGV) in processes performing timestamp verification.
• Network: Repeated or anomalous submissions of TimeStamp Response data to services that perform RFC 3161 verification, particularly from unexpected source IPs or with malformed DER-encoded payloads.
• Process: Unexpected termination or restart of services that use OpenSSL timestamp verification (e.g., code-signing daemons, PKI validation services); increased process crash rates correlated with TSR processing activity.

Update OpenSSL to a patched version immediately: 1.1.1ze or later, 3.0.19 or later, 3.3.6 or later, 3.4.4 or later, 3.5.5 or later, or 3.6.1 or later, depending on the installed branch (OpenSSL Advisory). Patches are available as GitHub commits across all affected branches and have been incorporated into downstream distributions including Red Hat, Ubuntu, Debian, SUSE, Alpine, FreeBSD, and Amazon Linux (Red Hat Errata). As a workaround, if applications do not require RFC 3161 timestamp verification, disabling or removing that functionality reduces exposure; however, patching is the recommended and definitive remediation. IBM products including InfoSphere Information Server, API Connect, Netezza Appliance, watsonx Orchestrate, and Instana Observability have also released fixes (IBM InfoSphere Advisory).

The vulnerability attracted notable attention partly because it was among 12 OpenSSL vulnerabilities discovered by an AI-assisted security research team (Aisle), which claimed a 12-for-12 detection rate on OpenSSL zero-days — a finding covered by Tom's Hardware, Heise, TechRadar, and cybersecurity news outlets (Tom's Hardware, Aisle Blog). The OpenSSL project acknowledged the high quality of the reports and constructive collaboration with the researchers. Community discussion on oss-security and OpenSSL mailing lists noted the low practical severity of this specific issue given the limited deployment of RFC 3161 timestamp verification (oss-sec).