VulnerabilityPublished 19 Sep 2026Updated 4 Nov 2026

CVE-2026-63374: AnyIO · TLSStream IDNA 2003 host name encoding enables potential TLS certificate spoofing

Affects gptmeSource GCVE Database

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Authoritative record:CVE-2026-63374· Critical 9.3

Not known to be exploited · CVSS 9.3 Critical : upgrade to 0.32.1 as a priority.

Data as of 4 Nov 2026, 21:27 UTC

CVSS 4.0 base score

9.3Critical

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

EPSS: 0.2% chance of exploitation in 30 days – higher than 21% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 0.32.1

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: High
Vulnerable system integrity: High
Vulnerable system availability: None
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

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

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, 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: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: None: 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.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: High: There is a total loss of confidentiality, resulting in all information within the Vulnerable System being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server.
Vulnerable system integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the vulnerable system. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the vulnerable system.
Vulnerable system availability: None: There is no impact to availability within the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 22 Sep 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 4 Nov 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 gptme to 0.32.1.

Affected software

Product	Affected	Fixed in
Homebrewgptme`pkg:brew/gptme`Other threats	Affected >=0.19.1 <0.32.1	Fixed in 0.32.1

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 AnyIO version 0.32.1 that fixes this vulnerability. Users should upgrade to this version to remediate the issue. As a workaround, host names can be encoded using the 'idna' package prior to establishing TLS connections. No other actions are currently required.

Description

AnyIO versions from 0.19.1 up to but not including 0.32.1 contain a vulnerability in TLSStream related to the use of IDNA 2003 host name encoding. This flaw allows an attacker to spoof TLS certificates for internationalized domain names by exploiting the encoding method, potentially causing clients to accept malicious certificates as valid. The issue is fixed in version 0.32.1. Users are advised to upgrade to this version or encode host names using the 'idna' package before connecting.

Impact

Services using internationalized domain names with vulnerable AnyIO versions may have their TLS connections spoofed by attackers who redirect connections and present certificates valid under IDNA 2003 encoding. This undermines the authenticity guarantees of TLS, potentially exposing clients to man-in-the-middle attacks without detection.

Summary

The vulnerability in AnyIO's TLSStream arises from the use of IDNA 2003 encoding for internationalized domain names (non-ASCII). An attacker who hijacks and redirects a TLS connection can obtain a legitimate certificate for the IDNA 2003 encoded domain and present it to the client, which will validate the certificate successfully. This enables potential TLS certificate spoofing attacks. The flaw affects AnyIO versions >=0.19.1 and <0.32.1 and is addressed in version 0.32.1.

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 4 Nov 2026, 20:33 UTC

Technical details

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