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TI-2026-66017 Aliases CVE-2026-103600GHSA-xp76-rp77-x5w9

Unbounded ASN.1 nesting depth causes process-terminating stack overflow

Priority MEDIUM 44CWE-674Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Attack requirements
None
Impact type
Denial of service
Confidentiality · integrity · availability
None · None · High
Fix status
Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA. Impact type from CWE-674.

Summary

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00359 29th percentileScored 2026-11-07
Fix Fixed bc-csharp (Legion of the Bouncy Castle Inc.): 2.7.0

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
Yes
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
Legion of the Bouncy Castle Inc.bc-csharpbefore 2.7.02.7.0Patch availableCNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:bouncycastle:bc-csharp:*:*:*:*:*:*:*:*before 2.7.0VulnerableLegion of the Bouncy Castle Inc.

Remediation

  • Fix · CNA bc-csharp (Legion of the Bouncy Castle Inc.) Fixed in 2.7.0

Fixed in the same release

Records fixed by the same vendor advisory or release, as the CNA lists them.

  • Release ·

    Legion of the Bouncy Castle bc-csharp 2.7.0

    21 records Highest priority Priority MEDIUM 8 MEDIUM, 13 LOW

    Other records, highest priority first

    • TI-2026-65844 MTI/A0 DHAgreement does not validate the peer's ephemeral valuePriority MEDIUM 47
    • TI-2026-66020 Unbounded HSS public key level count allows huge array allocation during signature verificationPriority MEDIUM 44
    • TI-2026-65849 Unbounded allocation from OpenPGP signature and user attribute subpacket lengthsPriority MEDIUM 44
    Show all 21 records →

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-103600
  2. 2026-10-03 Alias added: GHSA-xp76-rp77-x5w9
  3. 2026-10-28 CVSS score added · NVD

References

Patch 3

  • TI-2026-65844 MTI/A0 DHAgreement does not validate the peer's ephemeral value CVSS 4.0CRITICAL 9.1
  • TI-2026-66020 Unbounded HSS public key level count allows huge array allocation during signature verification CVSS 4.0HIGH 8.7
  • TI-2026-65849 Unbounded allocation from OpenPGP signature and user attribute subpacket lengths CVSS 4.0HIGH 8.7
  • TI-2026-65843 Unbounded CMP/CRMF password-based MAC iteration count allows CPU exhaustion CVSS 4.0HIGH 8.7
  • TI-2026-65841 DTLS handshake reassembler allocates buffer from unchecked 24-bit length CVSS 4.0HIGH 8.7
  • TI-2026-65846 Attribute certificate path validation does not verify the attribute certificate's signature CVSS 4.0HIGH 8.7
See all 21 →

Sources

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