Summary
CVE-2025-0343: Swift ASN.1 can crash when parsing maliciously formed BER/DER
Swift ASN.1 can be caused to crash when parsing certain BER/DER constructions. This crash is caused by a confusion in the ASN.1 library itself which assumes that certain objects can only be provided in either constructed or primitive forms, and will trigger a preconditionFailure if that constraint isn't met.
Importantly, these constraints are actually required to be true in DER, but that correctness wasn't enforced on the early node parser side so it was incorrect to rely on it later on in decoding, which is what the library did.
These crashes can be triggered when parsing any DER/BER format object. There is no memory-safety issue here: the crash is a graceful one from the Swift runtime. The impact of this is that it can be used as a denial-of-service vector when parsing BER/DER data from unknown sources, e.g. when parsing TLS certificates.
Many thanks to @baarde for reporting this issue and providing the fix.
Impact
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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Frequently Asked Questions
- What is CVE-2025-0343? CVE-2025-0343 is a low-severity security vulnerability in github.com/apple/swift-asn1 (swift), affecting versions <= 1.3.0. It is fixed in 1.3.1.
- Which versions of github.com/apple/swift-asn1 are affected by CVE-2025-0343? github.com/apple/swift-asn1 (swift) versions <= 1.3.0 is affected.
- Is there a fix for CVE-2025-0343? Yes. CVE-2025-0343 is fixed in 1.3.1. Upgrade to this version or later.
- Is CVE-2025-0343 exploitable, and should I be worried? Whether CVE-2025-0343 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2025-0343 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2025-0343? Upgrade
github.com/apple/swift-asn1to 1.3.1 or later.