CVE-2026-59886 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: Uncontrolled resource consumption when converting decoded REAL values
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-2026-59886.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-59886 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 univ.Real type converted its (mantissa, base, exponent) value to a Python float using exact big-integer exponentiation. A BER/CER/DER-encoded REAL value only a few bytes long can carry a very large exponent, causing this computation to attempt to materialize an astronomically large integer.
Any operation that triggers float conversion on such a decoded value — prettyPrint(), str(), comparison, arithmetic, or an explicit float() call — consumes excessive CPU and memory, hanging the process. Applications that decode untrusted ASN.1 data and then print, log, or compare the decoded objects are vulnerable to denial of service. Decoding alone does not trigger the issue.
Affected components
- pyasn1.type.univ.Real — float conversion (float() and everything built on it: prettyPrint(), str(), comparisons, arithmetic, int())
- Reachable through the pyasn1.codec.ber, cer, and der decoders, which produce Real objects from untrusted input; also via directly constructed Real values
The encoders and the native codec are not affected. Applications that never handle ASN.1 REAL values are not affected.
Patches
Fixed in pyasn1 0.6.4. Binary (base-2) values are now converted with math.ldexp(), and decimal (base-10) values with exponents beyond float range raise OverflowError without constructing huge intermediate integers. Existing behavior is preserved: out-of-range values raise OverflowError and prettyPrint() renders them as <overflow>.
Workarounds
Avoid converting, printing, or comparing decoded Real objects from untrusted sources; inspect the raw (mantissa, base, exponent) tuple instead.
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-2026-59886 is resolved across your whole dependency graph.
Workarounds
Stop feeding it untrusted input: reject or quarantine files and payloads from unverified sources until you can upgrade, restrict accepted formats to the ones you actually need, and run the parsing or decoding step in a least-privileged sandbox or short-lived worker so a crash or corrupted read cannot reach the rest of the process.
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.
This flaw in pyasn1, rated as Important, could lead to a denial of service in Red Hat products that process untrusted ASN.1 data. A remote attacker could send a specially crafted BER, CER, or DER encoded REAL value with a large exponent, causing applications to consume excessive resources during decoding operations…
When processing untrusted ASN.1 data with pyasn1, avoid calling prettyPrint(), str(), float(), int(), or performing comparisons or arithmetic on decoded Real (ASN.1 REAL type) objects. Instead, inspect the raw (mantissa, base, exponent) tuple directly. Where logging decoded ASN.1 structures is necessary, filter out or sanitize Real-typed values before conversion.Source: Red Hat security advisory for CVE-2026-59886 (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Ansible Automation Platform 2.5 for RHEL 8 | python3.12-pyasn1-0:0.6.4-1.el8ap | RHSA-2026:50319 |
| Red Hat Ansible Automation Platform 2.5 for RHEL 8 | automation-controller-0:4.6.32-1.el8ap | RHSA-2026:59135 |
| Red Hat Ansible Automation Platform 2.6 for RHEL 9 | python3.12-pyasn1-0:0.6.4-1.el9ap | RHSA-2026:50336 |
| Red Hat Ansible Automation Platform 2.6 for RHEL 9 | automation-controller-0:4.7.16-1.el9ap | RHSA-2026:59136 |
| Red Hat Enterprise Linux 10 | python-pyasn1-0:0.6.2-1.el10_2.1 | RHSA-2026:59243 |
| Red Hat Enterprise Linux 10.0 Extended Update Support | python-pyasn1-0:0.6.2-1.el10_0.2 | RHSA-2026:59238 |
| Red Hat Enterprise Linux 7 Extended Lifecycle Support | resource-agents-0:4.1.1-61.el7_9.24 | RHSA-2026:59329 |
| Red Hat Enterprise Linux 7 Extended Lifecycle Support | python-pyasn1-0:0.1.9-7.el7_9.3 | RHSA-2026:59240 |
Frequently Asked Questions
Is CVE-2026-59886 in your dependencies?
Find it across PyPI, including transitive dependencies.