CVE-2026-59886
ADVISORY - githubSummary
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 .
Workarounds
Avoid converting, printing, or comparing decoded Real objects from untrusted sources; inspect the raw (mantissa, base, exponent) tuple instead.
Common Weakness Enumeration (CWE)
Uncontrolled Resource Consumption
GitHub
3.9
CVSS SCORE
7.5high| Package | Type | OS Name | OS Version | Affected Ranges | Fix Versions |
|---|---|---|---|---|---|
| pyasn1 | pypi | - | - | <=0.6.3 | 0.6.4 |
CVSS:3 Severity and metrics
The CVSS metrics represent different qualitative aspects of a vulnerability that impact the overall score, as defined by the CVSS Specification.
The vulnerable component is bound to the network stack, but the attack is limited at the protocol level to a logically adjacent topology. This can mean an attack must be launched from the same shared physical (e.g., Bluetooth or IEEE 802.11) or logical (e.g., local IP subnet) network, or from within a secure or otherwise limited administrative domain (e.g., MPLS, secure VPN to an administrative network zone). One example of an Adjacent attack would be an ARP (IPv4) or neighbor discovery (IPv6) flood leading to a denial of service on the local LAN segment (e.g., CVE-2013-6014).
Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success when attacking the vulnerable component.
The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
The vulnerable system can be exploited without interaction from any user.
An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
There is no loss of confidentiality.
There is no loss of trust or accuracy within the impacted component.
There is a total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component.
Alpine
-
Debian
-
Ubuntu
-