VulnerabilityPublished 13 Aug 2026Updated 31 Oct 2026

CVE-2026-59884: Gcalcli · pyasn1 BER/CER/DER decoder denial of service via unbounded long-form tag IDs

Affects gcalcliSource GCVE Database

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Not known to be exploited · CVSS 7.5 High : upgrade to 4.5.1_13 soon.

Data as of 1 Nov 2026, 01:38 UTC

CVSS 3.1 base score

7.5High

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

Patch: Available – fixed in 4.5.1_13

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 13 Aug 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 31 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 gcalcli to 4.5.1_13.

Affected software

Product	Affected	Fixed in
Homebrewgcalcli`pkg:brew/gcalcli`Other threats	Affected >=4.3.0 <4.5.1_13	Fixed in 4.5.1_13

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A patch is available in gcalcli version 4.5.1_13 which includes pyasn1 version 0.6.4 with the fix. Users should upgrade to this version or later. As a workaround, limit the size of untrusted inputs passed to the decode() function to prevent excessive resource consumption. No other mitigations are indicated.

Description

A denial of service vulnerability exists in the pyasn1 BER/CER/DER decoder used by gcalcli, caused by unbounded long-form tag IDs that lead to excessive CPU consumption. The flaw allows crafted inputs to force the decoder to build very large integers, causing quadratic CPU cost growth and potential crashes on Python 3.11+ due to unhandled ValueError exceptions. This affects decoding of untrusted BER/CER/DER inputs in gcalcli versions 4.3.0 up to but not including 4.5.1_13. The issue is fixed in version 4.5.1_13 by limiting tag ID size and improving error handling.

Impact

This vulnerability allows denial of service by causing excessive CPU consumption when decoding crafted BER/CER/DER inputs, potentially leading to application unavailability. On Python 3.11+, it can also cause unhandled exceptions that may bypass error handling mechanisms. There is no impact on confidentiality or integrity reported. The vulnerability affects any application using the vulnerable pyasn1 decoders to process untrusted inputs.

Summary

The BER decoder in pyasn1, shared by CER and DER codecs, parses long-form tags by accumulating continuation octets without an upper bound on tag ID size. This allows an attacker to craft inputs that cause the decoder to build arbitrarily large integers, resulting in high CPU usage growing quadratically with input size (e.g., a ~1 MB input can consume over a minute of CPU). On Python 3.11 and later, oversized tag IDs can trigger unhandled ValueError exceptions during error message formatting, violating the expected PyAsn1Error contract and potentially bypassing caller error handling. The vulnerability affects the decode() and StreamingDecoder functions in pyasn1.codec.ber.decoder, as well as the cer and der decoders that inherit the same tag parsing logic. The pyasn1.type.tag module's Tag and TagSet representations can also raise ValueError when rendering oversized tag IDs. The encoders and pyasn1.codec.native codec are not affected. The issue is fixed in pyasn1 version 0.6.4 (bundled in gcalcli 4.5.1_13), which limits long-form tag IDs to 20 octets and rejects oversized tags with PyAsn1Error. Tag ID rendering was also hardened against Python's integer-to-string conversion limits. Workarounds include bounding the size of untrusted input before decoding.

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 1 Nov 2026, 01:38 UTC

Technical details

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