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CVE-2026-103262VulnerabilityPublished Updated

jupyterlab · tornado: CurlAsyncHTTPClient enforces no response-size limit — decompression bomb drives unbounded memory accumulation

Affects jupyterlabSource GCVE Database

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Authoritative record:CVE-2026-103262· High 8.7

Not known to be exploited · CVSS 8.7 High : upgrade to 4.6.4 soon.

Data as of 30 Oct 2026, 08:59 UTC

CVSS 4.0 base score
8.7High
How severe the flaw is on the 0–10 CVSS scale.
Patch
Available – fixed in 4.6.4
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 1 Oct 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq 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.

What to do

Upgrade jupyterlab to 4.6.4.

Affected software

ProductAffectedFixed in
Homebrewjupyterlabpkg:brew/jupyterlabOther threatsAffected
  • >=1.2.0 <4.6.4
Fixed in
  • 4.6.4

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 version 4.6.4 that addresses this issue by adding appropriate response size limits to CurlAsyncHTTPClient. Users should upgrade to version 4.6.4 or later to remediate this vulnerability. Until patched, avoid configuring Tornado to use CurlAsyncHTTPClient for fetching untrusted URLs with decompression enabled. There is no indication that other mitigations or configuration changes can fully prevent this issue in affected versions.

Description

CVE-2026-103262 is a high-severity vulnerability in Tornado's CurlAsyncHTTPClient where no response size limit is enforced during decompression, allowing a decompression bomb to cause unbounded memory growth. An attacker-controlled server can send a gzip-compressed payload that expands massively in memory, causing the client process to consume gigabytes of RAM and potentially be killed by the operating system's out-of-memory (OOM) killer. This issue affects Tornado versions from 1.2.0 up to but not including 4.6.4. The vulnerability is distinct from a previously fixed decompression bomb issue in SimpleAsyncHTTPClient, as CurlAsyncHTTPClient lacks the size checks present in that client. A fix is available in Tornado 4.6.4.

References

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