high CVSS 7.5 EPSS <0.1%

CVE-2026-30922·Python vulnerability

pyasn1 is a generic ASN.1 library for Python. Prior to 0.6.3, the `pyasn1` library is vulnerable to a Denial of Service (DoS) attack caused by uncontrolled recursion when decoding ASN.1 data with deeply nested structures. An attacker can supply a crafted payload containing thousands of nested `SEQUENCE` (`0x30`) or `SET` (`0x31`) tags with "Indefinite Length" (`0x80`) markers. This forces the decoder to recursively call itself until the Python interpreter crashes with a `RecursionError` or consumes all available memory (OOM), crashing the host application. This is a distinct vulnerability from CVE-2026-23490 (which addressed integer overflows in OID decoding). The fix for CVE-2026-23490 (`MAX_OID_ARC_CONTINUATION_OCTETS`) does not mitigate this recursion issue. Version 0.6.3 fixes this specific issue.

Severity
high
Software
Python
Fixed in
0.6.3
Published

How likely is exploitation

FIRST's Exploit Prediction Scoring System puts the probability of this CVE being exploited in the next 30 days at <0.1% — higher than 15% of all published CVEs. EPSS is an independent forecast of exploitation, not a severity rating: it says nothing about how much damage a successful attack does, which is what a CVSS score measures.

Read the two together. CVE-2026-30922 scores 7.5 on CVSS, so a successful attack would be serious — but at <0.1%, almost nobody is currently attempting it. That is a different situation from a flaw under mass exploitation, and it is usually the difference between patching on your next maintenance window and patching tonight.

Affected versions

Until: 0.6.3

Fixed in: 0.6.3

How to fix this CVE

Update the pyasn1 library to version 0.6.3 or later to patch the recursive ASN.1 decoding vulnerability. This fix prevents maliciously crafted payloads with deeply nested SEQUENCE or SET structures from triggering stack exhaustion or out-of-memory conditions. Users relying on Python's ASN.1 decoding functionality should prioritize this update to mitigate denial-of-service risks.

sudo dnf update python3-pyasn1-0.6.3

Defensia detects this vulnerability

How to check if you are affected

  1. Check the installed pyasn1 version: python3 -c 'import pyasn1; print(pyasn1.__version__)'
  2. Identify applications using pyasn1: pip3 show pyasn1 | grep Location, then search that path for imports
  3. Search application logs for RecursionError or MemoryError messages paired with ASN.1 decoding timestamps: grep -i 'recursion\|memoryerror' /var/log/application.log | grep -i 'asn\|der\|ber'
  4. Verify the patch: python3 -c 'import pyasn1; version_tuple = tuple(map(int, pyasn1.__version__.split("."))); print("Patched" if version_tuple >= (0, 6, 3) else "Vulnerable")'

FAQ

What is CVE-2026-30922?

CVE-2026-30922 is a denial-of-service vulnerability in pyasn1 where deeply nested ASN.1 SEQUENCE or SET structures with indefinite-length markers cause uncontrolled recursion, leading to stack overflow or memory exhaustion in the Python interpreter.

Is CVE-2026-30922 being actively exploited?

No, CVE-2026-30922 is not currently listed on CISA's Known Exploited Vulnerabilities catalog, and no public exploits have been disclosed.

What versions of Python are affected by CVE-2026-30922?

All pyasn1 versions prior to 0.6.3 are vulnerable. The issue affects any Python 3.x environment running an older pyasn1 release.

How do I check if my server is vulnerable to CVE-2026-30922?

Run `python3 -c 'import pyasn1; print(pyasn1.__version__)'` — if the version is below 0.6.3, your system is vulnerable.

Does Defensia detect CVE-2026-30922?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If pyasn1 is installed on a monitored server, CVE-2026-30922 will appear in your dashboard with remediation steps.

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References

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