CVE-2026-103600 Legion of the Bouncy Castle Inc. CVE debrief

Who should care

Defenders responsible for systems that use bc-csharp and parse untrusted ASN.1 encodings, including X.509 certificates and CRLs, CMS/PKCS#7, PKCS#8/PKCS#12, OCSP, and TLS Certificate messages, should prioritize patching or mitigating this vulnerability.

Why it matters

CVE-2026-103600 is a high-severity vulnerability in the ASN.1 parser of bc-csharp before 2.7.0, allowing remote unauthenticated attackers to cause denial of service via crafted ASN.1 encodings. Defenders should prioritize patching or mitigating this vulnerability, especially in systems that parse untrusted ASN.1.

• Denial of service via crafted ASN.1 encoding
• Potential for stack overflow and process termination
• Increased risk for systems parsing untrusted ASN.1

Technical summary

The ASN.1 parser in bc-csharp before 2.7.0 is vulnerable to uncontrolled recursion, which can lead to a denial-of-service attack. The vulnerability exists in the Asn1InputStream and Asn1StreamParser classes. This issue allows a remote unauthenticated attacker to cause a denial of service via a crafted ASN.1 encoding of deeply nested constructed elements. The vulnerability can be mitigated by patching bc-csharp to version 2.7.0 or later and implementing input validation and sanitization for ASN.1 encodings. The vulnerability affects systems that parse untrusted ASN.1, including X.509 certificates and CRLs, CMS/PKCS#7, PKCS#8/PKCS#12, OCSP, and TLS Certificate messages.

Defensive priority

Defenders should prioritize patching or mitigating this vulnerability, especially in systems that parse untrusted ASN.1, including X.509 certificates and CRLs, CMS/PKCS#7, PKCS#8/PKCS#12, OCSP, and TLS Certificate messages.

Recommended defensive actions

• Patch bc-csharp to version 2.7.0 or later
• Implement input validation and sanitization for ASN.1 encodings
• Monitor systems for potential denial-of-service attacks
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record and NVD vulnerability detail provide information on the vulnerability, its impact, and potential mitigations. The bc-csharp library's ASN.1 parser is vulnerable to uncontrolled recursion, which can lead to a denial-of-service attack.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.