Vulnerability · Published Oct 2, 2026 · Assigned by GitHub_M
CVE-2026-104874Multidict: Reference leak in CIMultiDict/MultiDict items-view union and subtraction
Medium 5.3
In plain English
A medium-severity memory leak in multidict from aio-libs. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 39% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Multidict is an implementation of a multidict data structure. From 6.7.0 until 6.9.1, the C extension's items-view reflected union operation, operand | d.items(), in multidict_itemsview_or2_impl and subtraction operation, d.items() - operand, in multidict_itemsview_sub1_impl fail to release new key-identity and value references returned for each operand element. Applications that perform these operations over attacker-influenced sequences can leak two strong references per element, and garbage collection cannot reclaim them, so repeated operations can cause unbounded process memory growth and denial of service. Forward union, intersection, non-tuple operand elements, and pure-Python builds are not affected by this reference leak. This issue is fixed in version 6.9.1.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| PyPI | multidict | 6.9.1 | GHSA-54p9-h82j-f925 |
| PyPI | multidict | 6.9.1 | PYSEC-2026-4244 |
| Ubuntu:22.04:LTS | python-multidict | no fix listed | UBUNTU-CVE-2026-104874 |
| Ubuntu:24.04:LTS | python-multidict | no fix listed | UBUNTU-CVE-2026-104874 |
| Ubuntu:26.04:LTS | python-multidict | no fix listed | UBUNTU-CVE-2026-104874 |
| Ubuntu:26.10 | python-multidict | no fix listed | UBUNTU-CVE-2026-104874 |
Affected products (as reported)
Weakness: CWE-401 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L