Zapros: Streaming decoders ignored the requested chunk size, allowing a single compressed response chunk to allocate unbounded memory (decompression bomb)

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

8.7 · 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 · score source

EPSS

• CVE-2026-61652: 0.44% estimated exploitation activity in the next 30 days; percentile 37.92 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact Denial of service via memory exhaustion. Affects all callers who streamed compressed responses relying on the chunk size — explicit (iterbytes(chunksize=...)) or the default — to bound memory. The decoder ignored that bound, so a chunk could be far larger than requested and a single compressed response could overflow memory. Patches Upgrade to 0.14.0 or later. The decoders now bound the output of each decompression step to the requested chunksize: gzip/deflate via zlib's maxlength + unconsumedtail, brotli via outputbufferlimit, and zstd via a bounded streamwriter. Peak memory during streaming decode is now proportional to chunksize for all supported encodings. Workarounds For unpatched versions: - Read the still-compressed body with Response.iterraw() / Response.asynciterraw(), which bypass the built-in decoders, and decompress it yourself with an explicit output-size bound (e.g. zlib's maxlength), aborting once a configured limit is exceeded. - Where feasible, send…

Published by the source

23 Sep 2026, 13:57 UTC

Last modified by the source

1 Oct 2026, 17:55 UTC

Source last checked

26 Oct 2026, 13:54 UTC

1. Revision 4 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-6cp7-3m3c-5x5c

2. Revision 3 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-6cp7-3m3c-5x5c

4. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-6cp7-3m3c-5x5c

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# Patch Next advisory brief: CVE-2026-61652

Advisory: Zapros: Streaming decoders ignored the requested chunk size, allowing a single compressed response chunk to allocate unbounded memory (decompression bomb)
IDs: CVE-2026-61652, GHSA-6cp7-3m3c-5x5c
Record: https://patchnext.com/advisories/cve-2026-61652 (revision 4, source checked 26 Oct 2026, 13:54 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: zapros 0.14.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI zapros: affected < 0.14.0; fixed in 0.14.0

## Suggested inspection (read-only)
- `python -m pip show zapros`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on zapros.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-6cp7-3m3c-5x5c (GitHub-reviewed advisory GHSA-6cp7-3m3c-5x5c lists affected ranges: PyPI zapros >=0 <0.14.0)
- Verified: https://osv.dev/vulnerability/GHSA-6cp7-3m3c-5x5c (OSV record GHSA-6cp7-3m3c-5x5c lists affected ranges: PyPI zapros >=0 <0.14.0 (fixed))

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