Summary
pyasn1: Uncontrolled resource consumption when converting decoded REAL values
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.
Workarounds
Avoid converting, printing, or comparing decoded Real objects from untrusted sources; inspect the raw (mantissa, base, exponent) tuple instead.
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.
Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.
CVE-2026-59886 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.6.4); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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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 .
Frequently Asked Questions
- What is CVE-2026-59886? CVE-2026-59886 is a high-severity uncontrolled resource consumption vulnerability in pyasn1 (pip), affecting versions <= 0.6.3. It is fixed in 0.6.4. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
- How severe is CVE-2026-59886? CVE-2026-59886 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of pyasn1 are affected by CVE-2026-59886? pyasn1 (pip) versions <= 0.6.3 is affected.
- Is there a fix for CVE-2026-59886? Yes. CVE-2026-59886 is fixed in 0.6.4. Upgrade to this version or later.
- Is CVE-2026-59886 exploitable, and should I be worried? Whether CVE-2026-59886 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-59886 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-59886? Upgrade
pyasn1to 0.6.4 or later.