VulnerabilityPublished 30 Oct 2026

CVE-2026-119195: pyasn1 has quadratic-time denial of service

Affects pyasn1Source GCVE Database

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Authoritative record:CVE-2026-119195· High 7.5

Not known to be exploited · CVSS 7.5 High : upgrade to 0.6.5 soon.

Data as of 31 Oct 2026, 01:55 UTC

CVSS 3.1 base score

7.5High

How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none

CVSS scores by source
CNA (GitHub_M)	CVSS 3.1	7.5

Patch: Available – fixed in 0.6.5

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: 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.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is 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 (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 29 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade pyasn1 to 0.6.5.

Affected software

Product	Affected	Fixed in
PyPIpyasn1	Affected <0.6.5	Fixed in 0.6.5

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AI-suggested

A fixed version of pyasn1 is available in version 0.6.5. Users should upgrade to pyasn1 0.6.5 or later to remediate this vulnerability. If upgrading is not immediately possible, applications should implement input validation or resource limits to restrict the size and complexity of ASN.1 inputs before decoding. No other vendor advisories indicate that no action is required or that the issue is mitigated by default.

Description

pyasn1 versions 0.6.4 and earlier contain a denial of service vulnerability due to quadratic-time processing when decoding constructed OCTET STRINGs, constructed character strings, and indefinite-length ANY types. This occurs because the decoder repeatedly concatenates fragments in a way that causes CPU time to grow quadratically with the number of fragments. An attacker supplying crafted ASN.1 input to an affected decoder can cause CPU exhaustion. The issue affects BER and CER decoding paths and certain non-DER constructed strings accepted by the DER decoder with specific schema. No confidentiality or integrity impact is reported.

Impact

An attacker who can supply crafted ASN.1 input to an application using pyasn1 0.6.4 or earlier can cause the decoder to consume excessive CPU resources due to quadratic-time string reassembly. This can lead to denial of service by exhausting CPU availability on the decoding worker. There is no impact on confidentiality or integrity. The severity is high with a CVSS v3.1 base score of 7.5, assuming unauthenticated network input is automatically decoded. The vulnerability does not affect all applications equally; exploitability depends on whether attacker-controlled ASN.1 input reaches the decoder without sufficient input validation or resource limits.

Summary

In pyasn1 version 0.6.4 and earlier, the BER and CER decoders for constructed OCTET STRINGs, constructed character strings, and indefinite-length ANY types perform repeated concatenations of decoded fragments using immutable byte strings. This leads to quadratic-time complexity in CPU usage relative to the number of fragments, as each concatenation copies an increasingly large prefix. The DER decoder rejects constructed OCTET STRINGs by default but accepts certain non-DER constructed strings when an asn1Spec schema is provided, exposing the same issue. The vulnerability allows an attacker to supply crafted ASN.1 input that causes excessive CPU consumption during decoding, potentially leading to denial of service. The problem is distinct from a previously fixed OID accumulation issue and was not addressed by the patch for that issue. The vulnerability is fixed in pyasn1 version 0.6.5.

CWE-407Inefficient Algorithmic Complexity (opens in a new tab)
Class weaknessLikelihood of exploit: Low
An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.
OWASP Cheat Sheets
File Upload (opens in a new tab)
OWASP ASVS 4.0.3
V12.1.1 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 31 Oct 2026, 01:55 UTC

WeaknessesCWE-407

Technical details

References

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