# CVE-2026-63570: Pkcs12Store.GetCertificateChain loops forever on cyclic issuer links

> Attackers can cause denial of service in applications using bc-csharp by supplying crafted PKCS#12 files with cyclic certificate issuer links.

- **Severity:** High 7.1 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 2 Oct 2026
- **Updated:** 2 Oct 2026
- **Also known as:** GHSA-g2c8-ppvq-rq73

## What is CVE-2026-63570?

CVE-2026-63570 is a high-severity denial of service vulnerability in Legion of the Bouncy Castle Inc. bc-csharp, published on 2 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

Loop with unreachable exit condition in Pkcs12Store.GetCertificateChain in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows an attacker who can supply a crafted PKCS#12 file to an application that loads it and requests a key entry's certificate chain to cause a denial of service, in which the call never returns and consumes CPU and memory until an OutOfMemoryException, via certificates whose issuer links form a cycle, for example two certificates whose AuthorityKeyIdentifier extensions each identify the other's public key. This happens because the chain-building loop stops only when no issuer is found or a certificate links to itself, and keeps no record of certificates already visited. The key-identifier links are followed without checking signatures.

Weakness: CWE-835 (Loop with Unreachable Exit Condition)

## Which versions are affected by CVE-2026-63570?

It affects 1 product.


Products: Bouncycastle Bc-Csharp.

## How do I fix CVE-2026-63570?

No fix has been published for CVE-2026-63570 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-63570 being exploited?

There is no known exploitation of CVE-2026-63570 in the wild and no public exploit code.

## Other vulnerabilities in Legion of the Bouncy Castle Inc. bc-csharp

- [CVE-2026-63569](https://insights.sbomify.com/CVE-2026-63569/): MTI/A0 DHAgreement does not validate the peer's ephemeral value (critical 9.1)
- [CVE-2026-103600](https://insights.sbomify.com/CVE-2026-103600/): Unbounded ASN.1 nesting depth causes process-terminating stack overflow (high 8.7)
- [CVE-2026-103603](https://insights.sbomify.com/CVE-2026-103603/): Unbounded HSS public key level count allows huge array allocation during signature verification (high 8.7)
- [CVE-2026-103604](https://insights.sbomify.com/CVE-2026-103604/): Quadratic-time escaping when converting X.509 distinguished names to strings (high 8.7)
- [CVE-2026-16000](https://insights.sbomify.com/CVE-2026-16000/): KCcmBlockCipher (DSTU 7624 CCM) tag not bound to nonce when no associated data is used (high 8.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-63570 and fix it if it is affected.

What it is: CVE-2026-63570 is a high-severity denial of service vulnerability in Legion of the Bouncy Castle Inc. bc-csharp, published on 2 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-63570 in the wild and no public exploit code.

Affected product: Legion of the Bouncy Castle Inc. bc-csharp. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-63570/ (Markdown: https://insights.sbomify.com/CVE-2026-63570/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63570
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63570
- OSV: https://osv.dev/vulnerability/CVE-2026-63570

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-63570/
Summaries are generated and may contain mistakes; the official description above is the record.