CVE-2026-116577VulnerabilityPublished 26 Oct 2026Updated 6 Nov 2026

Python tornado: Prior to 6.6, Tornado's HTTP header parser accepts obsolete line folding and repeatedly concatenates

Affects python-tornadoSource GCVE Database

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Authoritative record:CVE-2026-116577· Medium 5.3

Not known to be exploited · CVSS 5.3 Medium · fixed in 6.6 : update python-tornado when convenient.

Data as of 6 Nov 2026, 23:24 UTC

CVSS 3.1 base score

5.3Medium

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	5.3

EPSS: 0.3% chance of exploitation in 30 days – higher than 32% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 6.6

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

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

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: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 26 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 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–

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AI-suggested

Upgrade Tornado to version 6.6 or later, where this vulnerability is fixed. No other mitigations are indicated by the vendor advisory.

Description

Tornado, a Python web framework, has a vulnerability in its HTTP header parser prior to version 6.6. The parser accepts obsolete line folding and repeatedly concatenates short continuation lines, leading to quadratic CPU consumption on the IOLoop thread. An unauthenticated client can exploit this by sending a header block with many obsolete line-folding continuations, causing a denial of service by blocking other connections. This issue affects availability only and is fixed in Tornado version 6.6.

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 6 Nov 2026, 21:02 UTC

Technical details

References

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