CVE-2026-59884 is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in pyasn1. A fix is available for pyasn1 — see the affected versions and patch details below.
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 CVE-2026-59884.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-59884 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 390,807 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
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 | 0.6.4pip install --upgrade 'pyasn1==0.6.4' |
Affected Products
pyasn1pyasn1Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for pyasn1, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update pyasn1 to 0.6.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-59884 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
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.…
Update to pyasn1 version 0.6.4 or later when available for your product stream. The impact is limited to availability (denial of service) — an attacker cannot access or modify data. Applications that do not process untrusted ASN.1/BER input are at reduced risk.Source: Red Hat security advisory for CVE-2026-59884 (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat AI Inference Server 3.3 | rhaiis/model-opt-cuda-rhel9:1787601159 | RHSA-2026:59518 |
| Red Hat AI Inference Server 3.4 | rhaii/vllm-rocm-rhel9:1791856725 | RHSA-2026:83121 |
| Red Hat Enterprise Linux AI 3.3 | rhelai3/disk-image-cuda-rhel9:1788290314 | RHSA-2026:62335 |
| Red Hat Enterprise Linux AI 3.3 | rhelai3/bootc-aws-cuda-rhel9:1788273908 | RHSA-2026:62336 |
| Red Hat Hardened Images | jaeger-main-2.19.0-1.1.hum1 | RHSA-2026:40236 |
| Red Hat OpenShift AI 3.3 | rhoai/odh-llama-stack-core-rhel9:1789121286 | RHSA-2026:73987 |
| Red Hat OpenShift AI 3.4 | rhoai/odh-mlflow-rhel9:1787226790 | RHSA-2026:60520 |
Frequently Asked Questions
Is CVE-2026-59884 in your dependencies?
Find it across PyPI, including transitive dependencies.