# CVE-2026-97688: urllib3: Chunked Deflate streaming can enter an infinite loop > A malicious server can cause urllib3 to enter an infinite loop during chunked deflate decoding, leading to excessive CPU usage and denial of service. - **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 29 Sep 2026 - **Updated:** 29 Sep 2026 - **Also known as:** BELL-CVE-2026-97688, CLEANSTART-2026-AD44592, CLEANSTART-2026-BK97819, CLEANSTART-2026-BS13854, CLEANSTART-2026-GA47961, CLEANSTART-2026-TN63603, CLEANSTART-2026-WE83392, CLEANSTART-2026-ZK07015, DEBIAN-CVE-2026-97688, ECHO-3248-276e-35b8, GHSA-gh4c-6fx4-qh6g, MINI-28hh-f422-22x4, MINI-2rwc-x644-56pc, MINI-32xr-6558-89wp, MINI-3348-8m8g-fgqf, MINI-48mm-mmpw-2wm8, MINI-4q6j-g58g-rrjj, MINI-4xx6-jx86-55cx, MINI-65qv-3q53-5q7g, MINI-6f44-864f-9gxc, MINI-76q6-vjhh-4rw9, MINI-9qj8-f3w3-mv3v, MINI-c5rw-fphj-4m23, MINI-cr4h-pmp2-jx4j, MINI-cw82-8687-5gm2, MINI-f2h6-gwpf-qjjc, MINI-fjv4-vprr-75pm, MINI-fph7-3cjc-35gc, MINI-hh8x-857j-fwmp, MINI-hmfw-9x98-rh7h, MINI-hr75-p6rf-7pf3, MINI-m58q-q7mw-fwcp, MINI-m8w2-4722-pwmm, MINI-mfrq-rjf8-w4f4, MINI-mmwf-qjg6-9j33, MINI-mqjq-jprg-mmf4, MINI-p6c3-cm8r-xc6v, MINI-pj8m-vhv3-44rj, MINI-pprv-49hf-p7jw, MINI-qfww-627m-h5c6, MINI-r7jf-cj5c-7q52, MINI-w6g5-9vvj-x97j, MINI-xj22-vc79-274r, PYSEC-2026-4176, UBUNTU-CVE-2026-97688 ## What is CVE-2026-97688? CVE-2026-97688 is a medium-severity denial of service vulnerability in urllib3, published on 29 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official description urllib3 is an HTTP client library for Python. From 2.6.2 until 2.8.0, HTTPResponse.stream and HTTPResponse.read_chunked can enter an infinite loop because the Deflate decoder retains trailing bytes as unconsumed input after reaching end-of-stream and repeatedly decodes them without progress. The issue occurs when an untrusted server sends a chunked Deflate response whose decoded body exceeds a positive finite chunk size and whose encoded body has trailing bytes, specifically a response with Transfer-Encoding: chunked and Content-Encoding: deflate, content decoding enabled, and the positive finite amt=N streaming chunk size. The attack mechanism is that a malicious server returns a compressed chunked response with trailing bytes after the Deflate stream. The impact is excessive CPU usage and a request that does not complete, and network read timeouts do not interrupt the loop because no further socket read occurs. This issue is fixed in version 2.8.0. Weakness: CWE-835 (Loop with Unreachable Exit Condition) ## Which versions are affected by CVE-2026-97688? 3 open source packages ship an affected version, including urllib3. It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `urllib3` | PyPI | From 2.6.2 | 2.8.0 | | `urllib3` | PyPI | From 2.6.2 | 2.8.0 | | `urllib3` | PyPI | From 2.6.2 | 2.8.0 | Products: Python Urllib3. ## How do I fix CVE-2026-97688? Upgrade urllib3 to 2.8.0 or later. ## Is CVE-2026-97688 being exploited? There is no known exploitation of CVE-2026-97688 in the wild and no public exploit code. ## Other vulnerabilities in urllib3 - [CVE-2026-97689](https://insights.sbomify.com/CVE-2026-97689/): urllib3: HTTPResponse.stream()/read_chunked() buffers an unbounded chunk-size line into memory (high 8.9) - [CVE-2026-44432](https://insights.sbomify.com/CVE-2026-44432/): urllib3: Decompression-bomb safeguards bypassed in parts of the streaming API (high 8.9) - [CVE-2026-21441](https://insights.sbomify.com/CVE-2026-21441/): urllib3 vulnerable to decompression-bomb safeguard bypass when following HTTP redirects (streaming API) (high 8.9) - [CVE-2025-66418](https://insights.sbomify.com/CVE-2025-66418/): urllib3 allows an unbounded number of links in the decompression chain (high 8.9) - [CVE-2025-66471](https://insights.sbomify.com/CVE-2025-66471/): urllib3 Streaming API improperly handles highly compressed data (high 8.9) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-97688 and fix it if it is affected. What it is: CVE-2026-97688 is a medium-severity denial of service vulnerability in urllib3, published on 29 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. Exploitation: There is no known exploitation of CVE-2026-97688 in the wild and no public exploit code. Affected packages and fixed versions: - urllib3 (PyPI): affected from 2.6.2; fixed in 2.8.0 - urllib3 (PyPI): affected from 2.6.2; fixed in 2.8.0 - urllib3 (PyPI): affected from 2.6.2; fixed in 2.8.0 Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-97688/ (Markdown: https://insights.sbomify.com/CVE-2026-97688/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-97688 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-97688 - OSV: https://osv.dev/vulnerability/CVE-2026-97688 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-97688/ Summaries are generated and may contain mistakes; the official description above is the record.