CVE-2026-49853VulnerabilityPublished 14 Jul 2026Updated 6 Nov 2026

Python tornado: Prior to 6.5.6, SimpleAsyncHTTPClient shallow-copied redirected requests and removed only the Host

Affects python-tornadoSource GCVE Database

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Not known to be exploited · CVSS 7.7 High · fixed in 6.5.6 : patch python-tornado soon.

Data as of 6 Nov 2026, 23:24 UTC

CVSS 3.1 base score

7.7High

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

EPSS: 0.4% chance of exploitation in 30 days – higher than 38% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 6.5.6

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

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

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: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 14 Jul 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 6 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

Affected software

Product	Affected	Fixed in
Ubuntu 26.10python-tornado`pkg:deb/ubuntu/python-tornado?arch=source&distro=stonking`Other threats	Affected 6.5.4-0.1 – 6.5.5-5ubuntu1.2 6 affected builds	Fixed in–
Ubuntu 26.04 LTSpython-tornado`pkg:deb/ubuntu/python-tornado?arch=source&distro=resolute`Other threats	Affected 6.4.2-3 – 6.5.4-0.1ubuntu0.3 6 affected builds	Fixed in–
Ubuntu 24.04 LTSpython-tornado`pkg:deb/ubuntu/python-tornado?arch=source&distro=noble`Other threats	Affected 6.3.2-1 – 6.4.0-1ubuntu0.7 10 affected builds	Fixed in–
Ubuntu Pro 22.04 LTSpython-tornado`pkg:deb/ubuntu/python-tornado?arch=source&distro=esm-apps/jammy`Other threats	Affected 6.1.0-1build1 – 6.1.0-3ubuntu0.1~esm7 10 affected builds	Fixed in–
Ubuntu Pro 20.04 LTSpython-tornado`pkg:deb/ubuntu/python-tornado?arch=source&distro=esm-apps/focal`Other threats	Affected 5.1.1-4ubuntu1 – 6.0.3+really5.1.1-3ubuntu0.1~esm8 11 affected builds	Fixed in–
Ubuntu Pro 18.04 LTSpython-tornado`pkg:deb/ubuntu/python-tornado?arch=source&distro=esm-apps/bionic`Other threats	Affected 4.5.1-2.1~build2 – 4.5.3-1ubuntu0.2+esm5 10 affected builds	Fixed in–

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

AI-suggested

Upgrade Tornado to version 6.5.6 or later, where this issue is fixed. No other mitigation is indicated or required as the vulnerability is resolved by this official fix.

Description

A vulnerability in Python Tornado prior to version 6.5.6 affects the SimpleAsyncHTTPClient component. When handling redirected requests, it shallow-copied the requests but only removed the Host header, leaving sensitive headers such as Authorization and authentication details intact even when the redirect changed scheme, host, or port. This could lead to unintended credential leakage across different origins. The issue is fixed in version 6.5.6.

Impact

The vulnerability can lead to leakage of sensitive authentication headers during HTTP redirects that change the scheme, host, or port. This could allow an attacker controlling the redirect target to receive credentials or authentication tokens, resulting in potential unauthorized access or credential exposure. The CVSS score of 7.7 (high severity) reflects the network attack vector, low attack complexity, and high confidentiality impact without integrity or availability impact.

Summary

Tornado, a Python web framework and asynchronous networking library, had a security flaw in versions before 6.5.6 where SimpleAsyncHTTPClient shallow-copied redirected HTTP requests but failed to remove sensitive headers except for Host. Specifically, Authorization, auth_username, auth_password, and auth_mode headers remained present when redirects changed the scheme, host, or port, potentially exposing authentication credentials to unintended endpoints. This vulnerability is addressed by a fix in Tornado version 6.5.6.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 6 Nov 2026, 20:26 UTC

Technical details

References

Community reviews

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