VulnerabilityPublished 30 Oct 2026

CVE-2026-115927: Tornado · Event loop blocking and excess memory use from chunked bodies with many small chunks

Affects snakevizSource GCVE Database

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Authoritative record:CVE-2026-115927· Medium 5.3

Not known to be exploited · CVSS 5.3 Medium : upgrade to 2.2.2_7 when convenient.

Data as of 30 Oct 2026, 06:59 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 2.2.2_7

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 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 snakeviz to 2.2.2_7.

Affected software

Product	Affected	Fixed in
Homebrewsnakeviz`pkg:brew/snakeviz`Other threats	Affected >=2.2.0 <2.2.2_7	Fixed in 2.2.2_7

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 Tornado 6.6 that fixes this issue by yielding to the event loop periodically during body reading, combining small chunks, and optimizing memory usage. Users should upgrade to Tornado 6.6 or later. As workarounds, running Tornado behind a reverse proxy that buffers request bodies and forwards them with a Content-Length header instead of chunked encoding can mitigate the issue. Lowering the max_body_size configuration reduces the maximum blocking time and memory use per request but does not eliminate the vulnerability.

Description

Tornado HTTP servers are vulnerable to event loop blocking and excessive memory use when processing HTTP/1.1 chunked transfer encoding bodies composed of many small chunks. An attacker can send a request body with millions of 1-byte chunks, causing the event loop to block for extended periods (up to a minute for ~100 MB bodies) and consuming significantly more memory than the actual body size. This affects all Tornado HTTP servers that read request bodies without early rejection and also affects the SimpleAsyncHTTPClient when reading responses. The issue is fixed in Tornado 6.6 with changes to yield to the event loop periodically and optimize chunk handling.

Impact

The vulnerability allows an unauthenticated attacker to cause denial of service by blocking the Tornado event loop for extended periods, potentially up to a minute per request when sending chunked bodies with many small chunks. This blocks all other connections served by the same process. It also causes excessive memory consumption, roughly 20 times the size of the received bytes, which can further degrade service availability. The SimpleAsyncHTTPClient is similarly affected when reading malicious responses. No confidentiality or integrity impact is reported.

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 30 Oct 2026, 06:04 UTC

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