VulnerabilityPublished 31 Oct 2026

CVE-2026-119194: Aws shell · pyasn1 has quadratic CPU use in schemaless BER/CER/DER container decoding

Affects aws-shellSource GCVE Database

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Authoritative record:CVE-2026-119194· High 7.5

Not known to be exploited · CVSS 7.5 High.

Data as of 31 Oct 2026, 17:21 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

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

Affected software

Product	Affected	Fixed in
Homebrewaws-shell`pkg:brew/aws-shell`Other threats	Affected >=0.2.0	Fixed in–

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AI-suggested

Until a fix is available, avoid passing untrusted or attacker-controlled BER, CER, or DER data to schemaless decoding functions in pyasn1. Consider implementing input validation or rate limiting to mitigate potential CPU exhaustion attacks.

Description

CVE-2026-119194 is a high-severity vulnerability in pyasn1 used by aws-shell that causes quadratic CPU usage when decoding attacker-controlled BER, CER, or DER data without an ASN.1 schema. The flaw arises from inefficient handling of tag sets during schemaless decoding, allowing crafted inputs with many distinct long tag IDs to exhaust CPU resources and degrade service availability. No confidentiality or integrity impacts are reported.

Impact

The vulnerability allows an attacker to cause excessive CPU consumption by submitting specially crafted BER, CER, or DER encoded data to applications performing schemaless decoding with pyasn1. This can lead to denial of service through resource exhaustion, reducing service availability. There is no observed impact on confidentiality or integrity.

Summary

The vulnerability occurs in pyasn1 version 0.6.4 where the ConstructedPayloadDecoderBase._decodeComponentsSchemaless method inserts every decoded component's TagSet into a growing set, leading to quadratic CPU complexity when processing attacker-controlled BER, CER, or DER data with many distinct long tag IDs. This inefficiency is due to hash collisions causing repeated comparisons against an increasing number of tag sets. The issue affects schemaless decoding paths for BER, CER, and DER. A fix involves limiting the growth of the classification set to two distinct tag sets while preserving component order. Proof-of-concept code demonstrates that increasing the number of colliding components significantly raises CPU time required for decoding, impacting availability but not confidentiality or integrity.

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What to do

Affected software

Description

AI analysisMachine-generated, updated 31 Oct 2026, 17:21 UTC

Technical details

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