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CVE-2026-103603

7.5, high

Memory allocation with excessive size value in the HSS/LMS signature code (HssPublicKeyParameters, HssSignature) in Legion of the Bouncy…

NVD (opens in a new tab) CVE.org (opens in a new tab)
CVSS
7.5, high high CVSS v3.1
EPSS, next 30 days
0.5% higher than 42.9% of scored CVEs
Exploitation
No public evidence
Published
2 Oct 202627 days ago

Description

Memory allocation with excessive size value in the HSS/LMS signature code (HssPublicKeyParameters, HssSignature) in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a remote unauthenticated attacker who can supply both an HSS public key and a signature to cause a denial of service through memory exhaustion via a public key encoding with an excessive level count, because the level count L read when parsing an HSS public key was not checked against the RFC 8554 maximum of 8, and signature parsing then allocated an array of L - 1 entries before reading any further signature data. A single verification can commit up to about 17 GB of memory or fail with an OutOfMemoryException.

Details

Vendor
Legion of the Bouncy Castle Inc.
Product
bc-csharp
Weakness
CWE-789 (opens in a new tab)
Status
Analyzed
Updated
28 Oct 2026
Assigner
91579145-5d7b-4cc5-b925-a0262ff19630

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References 2

Patches and fixes 2

The kind is read from NVD's tags where present and from the shape of the URL otherwise, so treat it as a hint.

Other Legion of the Bouncy Castle Inc. CVEs

Every Legion of the Bouncy Castle Inc. CVE we hold

Same vendor in what we hold, not a known link between the flaws.

  • CVE-2026-17507 In Bouncy Castle for Java before 1.86, the MLS implementation (org.bouncycastle.mls) holds RFC 9420's uint32 leaf_index in a signed int,… EPSS 0.4% 7.5, high
  • CVE-2026-15999 Improper validation of integrity check value in the AES-CCM implementation (CcmParameters and CcmBlockCipher) in Legion of the Bouncy… EPSS 0.2% 7.5, high
  • CVE-2026-16000 Missing cryptographic step in the DSTU 7624 CCM mode implementation (KCcmBlockCipher) in Legion of the Bouncy Castle Inc EPSS 0.2% 7.5, high
  • CVE-2026-16001 Exposure of the message authentication key through the encryption keystream in the stream mode of IesEngine (an IesEngine constructed… EPSS 0.2% 7.5, high
  • CVE-2026-63566 Memory allocation with excessive size value in the DTLS handshake reassembly (DtlsReliableHandshake, DtlsReassembler) in Legion of the… EPSS 0.4% 7.5, high
  • CVE-2026-63567 Observable discrepancy in IesEngine.DecryptBlock in Legion of the Bouncy Castle Inc EPSS 0.5% 7.5, high
  • CVE-2026-63568 Legion of the Bouncy Castle Inc. bc-csharp Allocation of Resources Without Limits or Throttling Vulnerability EPSS 0.4% 7.5, high
  • CVE-2026-103600 Uncontrolled recursion in the ASN.1 parser (Asn1InputStream, Asn1StreamParser) in Legion of the Bouncy Castle Inc EPSS 0.3% 7.5, high

Beyond this page

Is CVE-2026-103603 in your network?

This page tells you how dangerous CVE-2026-103603 is out there. Whether it sits on one of your devices, only a scan of your own network can tell. That is what our systems do, every day, for the companies we protect.

  • EXYS7600 OCELOT

    Find it before attackers do

    Ocelot scans your network on a schedule and reports every vulnerability it finds by its CVE identifier, with its CVSS score and how many of your hosts are affected. A finding like CVE-2026-103603 comes with the devices to patch.

    Learn more about EXYS7600 OCELOT

  • EXYS7950 KONDRA

    Detect it if it's exploited

    Until the patch is applied, Kondra monitors your network, events and endpoints in real time. It keeps an inventory of the software installed on every endpoint, and its anomaly detection rules flag what an attacker does once inside.

    Learn more about EXYS7950 KONDRA
Check your exposure

Assembled from the NVD 2.0 API, the CISA Known Exploited Vulnerabilities Catalog and FIRST EPSS. Scores are as of our last collection on 29 Oct 2026, not the live upstream state.