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CVE-2026-86000 medium CVSS 5.3

Vulnerability in soupsieve (CVE-2026-86000)

Summary

Vulnerability in soupsieve (CVE-2026-86000). Risk of unauthorized operations or information disclosure. Exploitable via IDENTIFIER. Mitigation: upgrade to 2.9.0 or later.

Original description

The description as published by the source.

Summary

soupsieve compiles CSS selector strings with a set of hand-written regular expressions. The shared IDENTIFIER sub-pattern (also embedded in VALUE, and therefore in attribute selectors) places two adjacent quantified groups over overlapping character classes: (?:[classA]|ESC)+(?:[classB]|ESC)*, where both classes match ordinary identifier characters such as a. When a selector contains a long identifier/value run that must ultimately fail to match (e.g. an attribute value with no closing ], or an identifier followed by an invalid character), the regex engine backtracks across all O(n) ways to split the run between the + group and the * group, giving O(n²) parse time. A single attacker-controlled selector of a few kilobytes stalls the interpreter for many seconds of CPU; tens of kilobytes reach minutes.

Trust model (Q0)

The selector string is the input. It reaches this code via soupsieve.compile(), soupsieve.select/iselect/match/filter, and — most commonly — BeautifulSoup's soup.select(selector) / soup.select_one(selector), which delegate to soupsieve. This is exploitable in any application that passes a user-controlled CSS selector to BeautifulSoup/soupsieve (scrapers that accept selectors, no-code extraction tools, admin/query UIs). Applications that only use hard-coded selectors are not affected.

Root cause (exact anchors) — src/soupsieve/css_parser.py

# lines 122-126
IDENTIFIER = fr'''
(?:(?:-?(?:[^\x00-\x2f\x30-\x40\x5…

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-2026-86000 has been found in soupsieve.
Attackers can target a specific entry point like IDENTIFIER over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 5.3/10.
What to do: upgrade soupsieve to 2.9.0 or later.
If unsure, ask your IT team or search "soupsieve CVE-2026-86000" on the vendor's site.

CVE-2026-86000 (soupsieve) — CWE-400 / CVSS v3 5.3
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: IDENTIFIER / VALUE / re.match
Patched: 2.9.0 — 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-400) exists in soupsieve. Attackers reach the vulnerable code path via IDENTIFIER without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of soupsieve. Attack surface: IDENTIFIER / VALUE / re.match.

🔥 Severity

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

🔧 How to fix

Update to 2.9.0.

🛡️ 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 'soupsieve' . 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 'soupsieve' . | 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 soupsieve 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 soupsieve to 2.9.0

    ステージング環境で 2.9.0 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 soupsieve
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.9.0"}]}]

References

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