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CVE-2026-104874 medium CVSS 5.3

Vulnerability in multidict (CVE-2026-104874)

Summary

Vulnerability in multidict (CVE-2026-104874). Risk of unauthorized operations or information disclosure. Exploitable via multidict_itemsview_or2_impl. Mitigation: upgrade to 6.9.1 or later.

Original description

The description as published by the source.

Description

A reference leak in the items-view union and subtraction operators of aio-libs/multidict 6.7.0 through 6.9.0 (C extension) lets a remote client drive unbounded, unreclaimable memory growth by having each operand element leak one key-identity object and one value object. The reflected-union path (operand | d.items(), multidict_itemsview_or2_impl) and the subtraction path (d.items() - operand, multidict_itemsview_sub1_impl) parse each element into new strong references but release only the tuple wrapper, never the identity and value. Servers in the aio-libs stack build these views over attacker-supplied HTTP headers and query strings, so the operand size is under remote control. Forced garbage collection does not recover the leaked objects, so resident memory rises monotonically until the process is killed.

Root Cause

_multidict_itemsview_parse_item() returns new references: a fresh identity via md_calc_identity() and a fresh value via Py_NewRef(). The or2_impl first parse loop requests both but clears only arg:

// views.h:565 — or2_impl first parse loop
while ((st = PyIter_NextItem(iter, &arg)) > 0) {
    int tmp = _multidict_itemsview_parse_item(
        self, arg, &identity, NULL, &value);   // identity + value: new refs
    if (tmp < 0) goto fail;
    else if (tmp > 0) {
        if (_set_add(tmp_set, identity, value) < 0) goto fail;
    }
    Py_CLEAR(arg);                             // :575 clears arg ONLY
}

`_set…

Source: NIST National Vulnerability Database NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-104874 has been found in multidict.
Attackers can target a specific entry point like multidict_itemsview_or2_impl over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 5.3/10.
What to do: upgrade multidict to 6.9.1 or later.
If unsure, ask your IT team or search "multidict CVE-2026-104874" on the vendor's site.

CVE-2026-104874 (multidict) — CWE-401 / CVSS v3 5.3
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: multidict_itemsview_or2_impl / multidict_itemsview_sub1_impl / or2_impl / arg
Patched: 6.9.1 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-401) exists in multidict. Attackers reach the vulnerable code path via multidict_itemsview_or2_impl without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of multidict. Attack surface: multidict_itemsview_or2_impl / multidict_itemsview_sub1_impl / or2_impl / arg.

🔥 Severity

Severity: Medium (CVSS 5.3/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 6.9.1.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'multidict' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'multidict' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で multidict を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade multidict to 6.9.1

    ステージング環境で 6.9.1 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

pip multidict
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.9.1"}]}]

References

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