CVE-2026-44378: 
Botan vulnerability analysis and mitigation

CVE-2026-44378 is a denial-of-service vulnerability in Botan, a C++ cryptography library, caused by quadratic complexity when parsing certain BER indefinite length encodings. Prior to version 3.12.0, the parser accepted indefinite length encodings even in structures required to use DER encoding (which prohibits such encodings), allowing an attacker to trigger excessive CPU consumption. The vulnerability was published on May 27, 2026, and fixed in Botan 3.12.0. It carries a CVSS v3.1 base score of 7.5 (High) and a CVSS v4.0 base score of 6.9 (Medium) (GitHub Advisory).

The root cause is classified as CWE-407 (Inefficient Algorithmic Complexity): certain patterns of indefinite length encodings in BER-encoded ASN.1 data trigger quadratic worst-case behavior in Botan's parser. Because the library accepted indefinite length encodings even in DER-required contexts, an attacker can craft malicious ASN.1 structures (e.g., X.509 certificates, OCSP responses) that cause the parser to perform an exponentially growing number of operations relative to input size. No authentication or user interaction is required — any network-accessible service that processes attacker-supplied ASN.1 data is potentially vulnerable. The vulnerability was discovered by researcher Yt Sun and reported to the Botan project (GitHub Advisory).

Successful exploitation results in a CPU-based denial of service, causing the affected application to become unresponsive or crash. There is no impact on confidentiality or integrity — only availability is affected. Any service that processes attacker-controlled ASN.1 data (such as TLS certificate validation, OCSP response parsing, or other PKI operations) using a vulnerable version of Botan is at risk (GitHub Advisory).

1. Identify target: Locate a network-accessible service that uses Botan (version < 3.12.0) to parse ASN.1-encoded data, such as a TLS server performing certificate validation or an OCSP responder.
2. Craft malicious BER data: Construct an ASN.1 structure (e.g., an X.509 certificate or OCSP response) containing nested or repeated indefinite length encodings in fields that are normally required to use DER encoding.
3. Submit the payload: Send the crafted BER-encoded data to the target service (e.g., present the malicious certificate during a TLS handshake, or submit it to a certificate parsing endpoint).
4. Trigger quadratic parsing: The Botan BER parser processes the indefinite length encodings with quadratic complexity, causing CPU exhaustion and rendering the service unresponsive or crashing it (GitHub Advisory).

• Network: Unusual or repeated connections to services that process ASN.1/X.509 data (TLS endpoints, OCSP responders) from unexpected sources; large or malformed certificate/OCSP payloads in network captures.
• Process: Sustained high CPU utilization by the application process using Botan, particularly during TLS handshake or certificate validation phases.
• Logs: Application logs showing timeouts, crashes, or errors during ASN.1/BER parsing; repeated failed TLS handshakes or certificate validation errors from the same source IP.

The primary remediation is to upgrade Botan to version 3.12.0 or later, which enforces strict DER encoding requirements and rejects indefinite length encodings in DER-required contexts. As a temporary workaround, operators can implement input validation and limits on BER data complexity or parsing time at the application or network layer, and consider running parsers with CPU/memory resource constraints. Services that do not need to accept externally supplied ASN.1 data should restrict such input at the network perimeter (GitHub Advisory).