CVE-2026-97689urllib3: HTTPResponse.stream()/read_chunked() buffers an unbounded chunk-size line into memory
Updated under an hour ago ()
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It affects urllib3 and 1 other product. Add what you run to find out whether that includes you.
EPSS puts the chance of exploitation in the next 30 days at 0.29%, higher than 20% of scored CVEs.
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urllib3 is an HTTP client library for Python. From 1.10.3 until 2.8.0, the HTTPResponse.read_chunked and HTTPResponse.stream methods can allocate unbounded memory because the streaming chunk parser buffers the chunk-size field until newline or EOF without a length bound. The trigger is that a malicious server returns Transfer-Encoding: chunked followed by a very long run of bytes without a newline. The attack mechanism is that a malicious HTTP server sends a very long unterminated chunk-size line. The impact is that unbounded memory allocation can exhaust the client process. This issue is fixed in version 2.8.0.
- CVSS
- 8.9 HIGH (v4.0, CNA)CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H
- Weakness (CWE)
- CWE-770
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- 0.29% (percentile 20)
- Assigned by
- GitHub_M
- NVD analysis
- Analyzed
- Record last updated
- Sep 29, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
urllib3 urllib3 urllib3:urllib3 (from the name) | from 1.10.3, < 2.8.0 | CNA record |
python urllib3 python:urllib3 | from 1.10.3 before 2.8.0 | NVD |
References
- https://github.com/urllib3/urllib3/security/advisories/GHSA-vxq7-64xx-v4gwx-refsource-confirm, mitigation, vendor-advisory
- https://github.com/urllib3/urllib3/commit/cd770b059b543be29298ea5c52afb0b1b090f5edx-refsource-misc, patch
- https://github.com/urllib3/urllib3/releases/tag/2.8.0x-refsource-misc, release-notes
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.