GHSA-m4p7-r5rc-7g4j is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in pyasn1. O3 Security confirms whether GHSA-m4p7-r5rc-7g4j is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
pyasn1 BER/CER/DER decoder denial of service via unbounded long-form tag IDs
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-m4p7-r5rc-7g4j.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-m4p7-r5rc-7g4j plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 0 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
pyasn1Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Impact
The BER decoder (shared by the CER and DER codecs) parses long-form tags by accumulating continuation octets in a loop with no upper bound on the size of the tag ID. A crafted input can force the decoder to build an arbitrarily large integer, with CPU cost growing quadratically in input size — a ~1 MB input consumes over a minute of CPU. On Python 3.11+, the oversized tag ID can also trigger an unhandled ValueError (integer string conversion limit) while the decoder formats error messages, violating the documented PyAsn1Error contract and potentially bypassing caller error handling.
Any application decoding untrusted BER/CER/DER input is affected.
Affected components
pyasn1.codec.ber.decoder—decode()andStreamingDecoderpyasn1.codec.cer.decoderandpyasn1.codec.der.decoder, which inherit the same tag parsingpyasn1.type.tag—Tag/TagSetreprs could raiseValueErrorwhen rendering oversized tag IDs (reachable through decoder error paths)
The encoders and the pyasn1.codec.native codec are not affected.
Patches
Fixed in 0.6.4. Long-form tag IDs are now limited to 20 octets (140-bit tag IDs, matching the existing OID arc limit); oversized tags are rejected with PyAsn1Error. Tag ID rendering in reprs and error messages was additionally hardened against the interpreter's integer-to-string conversion limit.
Workarounds
Bound the size of untrusted input passed to decode() before calling it.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | pyasn1 | all versions | 0.6.4 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for pyasn1. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update pyasn1 to 0.6.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-m4p7-r5rc-7g4j is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-m4p7-r5rc-7g4j is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-m4p7-r5rc-7g4j. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
A flaw was found in pyasn1's BER decoder. The decoder parses long-form tags by accumulating continuation octets without an upper bound, allowing crafted input to force construction of an arbitrarily large integer with quadratic CPU cost. On Python 3.11+, this can also trigger unhandled ValueError exceptions.…
Frequently Asked Questions
Is GHSA-m4p7-r5rc-7g4j in your dependencies?
O3 detects GHSA-m4p7-r5rc-7g4j across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.