bc-csharp: Memory Allocation with Excessive Size Value
CVE-2026-63566 is a high-severity memory allocation with excessive size value vulnerability in bc-csharp from Legion of the Bouncy Castle, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists version 2.7.0 as the first without the flaw, so updating bc-csharp to that release or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.43% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update bc-csharp to 2.7.0 or a later version.
- Read the advisory on github.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Legion of the Bouncy Castle | bc-csharp | before 2.7.0 | 2.7.0 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- NoneNothing can be modified.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 8.7 | High | CNA |
| CVSS 3.1 | 7.5 | High | NVD |
Official description
Memory allocation with excessive size value in the DTLS handshake reassembly (DtlsReliableHandshake, DtlsReassembler) in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a remote unauthenticated DTLS peer to cause a denial of service through memory exhaustion via crafted handshake message fragments, because the reassembly buffer for each incoming handshake message was allocated at the 24-bit length declared in the fragment header, without the check against the peer's maximum handshake message size that TLS already applied. A fragment carrying no payload can force an allocation of almost 16 MB, for each of up to 16 pending messages per handshake, before the handshake is authenticated. DTLS servers and DTLS clients are both affected; TLS is not.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Memory Allocation with Excessive Size Value
The product allocates memory based on an untrusted, large size value, but it does not ensure that the size is within expected limits, allowing arbitrary amounts of memory to be allocated.
How developers prevent this class of flaw
- Perform adequate input validation against any value that influences the amount of memory that is allocated. Define an appropriate strategy for handling requests that exceed the limit, and consider supporting a configuration option so that the administrator can extend the amount of memory to be used if necessary.
- Run your program using system-provided resource limits for memory. This might still cause the program to crash or exit, but the impact to the rest of the system will be minimized.
More Memory Allocation with Excessive Size Value vulnerabilities (CWE-789)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
Other vulnerabilities in bc-csharp
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Recent Memory Allocation with Excessive Size Value vulnerabilities
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