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Medium, CVSS 6.9amended

joserfc: Compact JWS size guard allocates attacker-controlled segments before rejection

CVE-2026-119284GHSA-9pg5-8c7x-5hfx

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (joserfc 1.7.6), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • PyPI joserfc

    Affected
    < 1.7.6
    Fixed in
    1.7.6

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
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 · score source
EPSS
  • CVE-2026-119284: 0.19% estimated exploitation activity in the next 30 days; percentile 8.95 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary joserfc 1.7.4 defines compact-JWS header, payload, and signature limits, but calls `value.split(b".")` before validating them. Python `bytes.split()` copies the attacker-controlled segments, so the current guard allocates roughly one complete payload before rejecting it.

Reproduction ```bash .venv-research/bin/python 06-practical-testing/preauth-memory-profile.py ``` The input is resident before a fork-isolated verifier runs, and every signature is invalid. | Input | Peak RSS delta | Amplification | Result | |---:|---:|---:|---| | 1 MiB | 1.11 MiB | 1.11× | size rejected | | 4 MiB | 4.04 MiB | 1.01× | size rejected | | 8 MiB | 8.04 MiB | 1.01× | size rejected | | 16 MiB | 16.04 MiB | 1.00× | size rejected | | 32 MiB | 31.74 MiB | 0.99× | size rejected | | 64 MiB | 63.80 MiB | 1.00× | size rejected | The unconstrained profile is the primary evidence: joserfc allocates an additional attacker-sized object before producing its intended `ExceededSizeError`. A separate…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from osv record GHSA-9pg5-8c7x-5hfx

  2. Revision 1 · created ·

    Published from ghsa record GHSA-9pg5-8c7x-5hfx

Agent brief

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# Patch Next advisory brief: CVE-2026-119284

Advisory: joserfc: Compact JWS size guard allocates attacker-controlled segments before rejection
IDs: CVE-2026-119284, GHSA-9pg5-8c7x-5hfx
Record: https://patchnext.com/advisories/cve-2026-119284 (revision 2, source checked 31 Oct 2026, 06:15 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: joserfc 1.7.6. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI joserfc: affected < 1.7.6; fixed in 1.7.6

## Suggested inspection (read-only)
- `python -m pip show joserfc`: 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 joserfc.
- 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-9pg5-8c7x-5hfx (GitHub-reviewed advisory GHSA-9pg5-8c7x-5hfx lists affected ranges: PyPI joserfc >=0 <1.7.6)
- Verified: https://osv.dev/vulnerability/GHSA-9pg5-8c7x-5hfx (OSV record GHSA-9pg5-8c7x-5hfx lists affected ranges: PyPI joserfc >=0 <1.7.6 (fixed))

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