Legion of the Bouncy Castle bc-csharp up to 2.6.x ASN.1 Parser recursion

Summaryinfo

A vulnerability, which was classified as problematic, has been found in Legion of the Bouncy Castle bc-csharp up to 2.6.x. This impacts an unknown function of the component ASN.1 Parser. The manipulation leads to recursion. This vulnerability is referenced as CVE-2026-103600. Remote exploitation of the attack is possible. No exploit is available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in Legion of the Bouncy Castle bc-csharp up to 2.6.x and classified as problematic. This issue affects an unknown functionality of the component ASN.1 Parser. The manipulation with an unknown input leads to a recursion vulnerability. Using CWE to declare the problem leads to CWE-674. The product does not properly control the amount of recursion that takes place, consuming excessive resources, such as allocated memory or the program stack. Impacted is availability. The summary by CVE is:

Uncontrolled recursion in the ASN.1 parser (Asn1InputStream, Asn1StreamParser) in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a remote unauthenticated attacker to cause a denial of service via a crafted ASN.1 encoding of deeply nested constructed elements (for example SEQUENCE inside SEQUENCE, in definite-length DER or indefinite-length BER form), because each nesting level is parsed by a further recursive call with no bound on depth. About 2,000 levels (8 KB of DER) are enough to exhaust a 1.5 MB thread stack, the .NET main-thread default on Windows, and raise a StackOverflowException, which .NET cannot catch and which terminates the whole process; on threads with larger stacks, parse time instead grows quadratically with depth (about 9 seconds of CPU for a 64 KB input). Any path that parses untrusted ASN.1 is exposed, including X.509 certificates and CRLs, CMS/PKCS#7, PKCS#8/PKCS#12, OCSP and TLS Certificate messages.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-103600 since 10/01/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. The technical details are unknown and an exploit is not publicly available. The attack technique deployed by this issue is T1499 according to MITRE ATT&CK.

Upgrading to version 2.7.0 eliminates this vulnerability.

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Productinfo

Vendor

• Legion of the Bouncy Castle

Name

• bc-csharp

Version

• 2.0
• 2.1
• 2.2
• 2.3
• 2.4
• 2.5
• 2.6

CPE 2.3info

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CPE 2.2info

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