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Fencer Vulns
high 7.5

CVE-2025-0343 json

CVE-2025-0343: Swift ASN.1 can crash when parsing maliciously formed BER/DER

published 2025-01-14 21 mo ago modified 2026-06-17 4 mo ago also EUVD-2025-0068 , GHSA-w8xv-rwgf-4fwh

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 28%
public exploits
0
none known

Summary

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.

Patch / fix

  • swift github.com/apple/swift-asn1 1.3.1
  • Swift Project Swift ASN1 1.3.1

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
21 mo ago

Exploit prediction

0.34% chance of exploitation in the next 30 days, higher than 28% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CISA ADP 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
swift github.com/apple/swift-asn1
<1.3.1
1.3.1

Affected products

  • Swift Project Swift ASN1

Classification

Weakness
  • CWE-228 Improper Handling of Syntactically Invalid Structure

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.