VulnerabilityPublished 13 Aug 2026Updated 29 Oct 2026

CVE-2026-91992: Tornado · CurlAsyncHTTPClient leaks per-request credentials on handle reuse

Affects sickchillSource GCVE Database

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Authoritative record:CVE-2026-91992· High 8.2

Not known to be exploited · CVSS 8.2 High : upgrade to 2024.3.1_6 soon.

Data as of 30 Oct 2026, 07:30 UTC

CVSS 4.0 base score

8.2High

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

Patch: Available – fixed in 2024.3.1_6

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

Attack Vector: Network
Attack Complexity: High
Attack Requirements: Present
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: High
Vulnerable system integrity: None
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: High: The successful attack depends on the evasion or circumvention of security-enhancing techniques in place that would otherwise hinder the attack. These include: Evasion of exploit mitigation techniques, for example, circumvention of address space randomization (ASLR) or data execution prevention (DEP) must be performed for the attack to be successful; Obtaining target-specific secrets. The attacker must gather some target-specific secret before the attack can be successful. A secret is any piece of information that cannot be obtained through any amount of reconnaissance. To obtain the secret the attacker must perform additional attacks or break otherwise secure measures (e.g. knowledge of a secret key may be needed to break a crypto channel). This operation must be performed for each attacked target.
Attack Requirements: Present: The successful attack depends on the presence of specific deployment and execution conditions of the vulnerable system that enable the attack. These include: a race condition must be won to successfully exploit the vulnerability (the successfulness of the attack is conditioned on execution conditions that are not under full control of the attacker, or the attack may need to be launched multiple times against a single target before being successful); the attacker must inject themselves into the logical network path between the target and the resource requested by the victim (e.g. vulnerabilities requiring an on-path attacker).
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: None: There is no loss of integrity within 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 15 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 29 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 sickchill to 2024.3.1_6.

Affected software

Product	Affected	Fixed in
Homebrewsickchill`pkg:brew/sickchill`Other threats	Affected >=2023.5.30 <2024.3.1_6	Fixed in 2024.3.1_6

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

Description

# CurlAsyncHTTPClient leaks per-request credentials on handle reuse ## Summary `CurlAsyncHTTPClient` pools and reuses `pycurl` handles across requests but does not reset them between requests, and several per-request options are applied with no clearing branch. As a result, sensitive state set by one request persists onto a later request on the same client that does not set it. Two credential vectors are demonstrated below — a client TLS certificate (`SSLCERT`/`SSLKEY`) and proxy basic-auth credentials (`PROXYUSERPWD`) — both leaking to a different, unintended host. This affects all released versions through 6.5.6. ## Details In `tornado/curl_httpclient.py`, handles are created once and returned to a free list for reuse (`_process_queue` pops the handle at line 200, `_finish` re-appends it at line 245), and `_curl_setup_request` is never preceded by `curl.reset()`. The function clears *some* carried-over state on the reused handle — `unsetopt(PROXYUSERPWD)` in the no-proxy branch (line 394), `unsetopt(USERPWD)` when no auth is set (line 495), and the HTTP-method flag reset (lines 428-432) — but other options have no equivalent clearing path and persist until a later request sets them again. **Vector A — client TLS certificate (`SSLCERT`/`SSLKEY`).** Set-only, no clearing branch: ```python # tornado/curl_httpclient.py (v6.5.6), lines 498-502 if request.client_cert is not None: curl.setopt(pycurl.SSLCERT, request.client_cert) if request.client_key is not None: curl.setopt(pycurl.SSLKEY, request.client_key) ``` A request that sets `client_cert` leaves the certificate on the handle; a later request without `client_cert` presents it during its TLS handshake. **Vector B — proxy credentials (`PROXYUSERPWD`).** `PROXYUSERPWD` is set only inside the credentials branch and unset only in the no-proxy `else` branch: ```python # tornado/curl_httpclient.py (v6.5.6), lines 371-394 if request.proxy_host and request.proxy_port: curl.setopt(pycurl.PROXY, request.proxy_host) curl.setopt(pycurl.PROXYPORT, request.proxy_port) if request.proxy_username: # only place PROXYUSERPWD is set ... curl.setopt(pycurl.PROXYUSERPWD, credentials) ... else: try: curl.unsetopt(pycurl.PROXY) except TypeError: curl.setopt(pycurl.PROXY, "") curl.unsetopt(pycurl.PROXYUSERPWD) # only place it is unset ``` A request that sets a *new* `proxy_host` without `proxy_username` updates `PROXY`/`PROXYPORT` but never reaches the `else`, so the previous request's credentials persist and are sent to the new proxy. The same class also affects `INTERFACE` (lines 365-366: set only when `request.network_interface` is truthy, with no clearing branch), which is a lower-severity instance — a later request can be bound to a network interface it did not request. A single fix addresses all three (see Mitigation). ## PoC Both reproduce against the pinned release using public API only (`CurlAsyncHTTPClient`, `HTTPRequest`, and the documented per-request arguments). ### Vector A — client TLS certificate The two servers listen on different ports, so request B opens a fresh TCP+TLS connection; the certificate can only reach server 2 via the persisted handle option, not connection or session reuse. ``` python3 -m venv venv ./venv/bin/pip install "tornado==6.5.6" pycurl cryptography ./venv/bin/python poc_client_cert.py ``` ```python import asyncio import datetime import ipaddress import os import socket import ssl import sys import tempfile import threading from cryptography import x509 from cryptography.x509.oid import NameOID, ExtendedKeyUsageOID from cryptography.hazmat.primitives import hashes, serialization from cryptography.hazmat.primitives.asymmetric import rsa from tornado.httpclient import HTTPRequest from tornado.curl_httpclient import CurlAsyncHTTPClient def _key(): return rsa.generate_private_key(public_exponent=65537, key_size=2048) def _ca(): key = _key() name = x509.Name([x509.NameAttribute(NameOID.COMMON_NAME, "PoC-CA")]) now = datetime.datetime.now(datetime.timezone.utc) cert = ( x509.CertificateBuilder() .subject_name(name).issuer_name(name) .public_key(key.public_key()) .serial_number(x509.random_serial_number()) .not_valid_before(now - datetime.timedelta(minutes=1)) .not_valid_after(now + datetime.timedelta(days=1)) .add_extension(x509.BasicConstraints(ca=True, path_length=None), critical=True) .sign(key, hashes.SHA256()) ) return cert, key def _leaf(cn, ca_cert, ca_key, ips=None, client=False): key = _key() name = x509.Name([x509.NameAttribute(NameOID.COMMON_NAME, cn)]) now = datetime.datetime.now(datetime.timezone.utc) b = ( x509.CertificateBuilder() .subject_name(name).issuer_name(ca_cert.subject) .public_key(key.public_key()) .serial_number(x509.random_serial_number()) .not_valid_before(now

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