Vulnerability in soupsieve (CVE-2026-85999)
Summary
Vulnerability in soupsieve (CVE-2026-85999). Risk of unauthorized operations or information disclosure. Exploitable via selector_iter. Mitigation: upgrade to 2.9.0 or later.
Original description
The description as published by the source.
Summary
Before tokenizing, selector_iter trims leading/trailing whitespace and comments by running two regexes over the whole raw selector with .search(). The trailing one, RE_WS_END = re.compile(r'{WSC}*$'), is anchored only at the end ($), not the start. Because .search() retries the pattern at every offset, a long run of whitespace or CSS comments that is not sitting exactly at the end of the string makes each retry greedily consume the run and then fail $, producing O(n²) time. This triggers on perfectly valid selectors — e.g. a descendant combinator with a long whitespace gap, a + " "*n + b — so no malformed input is required. A single valid ~20 KB selector stalls the interpreter for ~10 s of CPU.
Trust model (Q0)
The selector string is the input, reaching this code via soupsieve.compile(), the soupsieve.select/iselect/match/filter helpers, and BeautifulSoup's soup.select(selector) / soup.select_one(selector). Exploitable wherever an application passes a user-controlled CSS selector to BeautifulSoup/soupsieve. Applications using only hard-coded selectors are unaffected.
Root cause (exact anchors) — src/soupsieve/css_parser.py
# line 185-186
RE_WS_BEGIN = re.compile(fr'^{WSC}*') # anchored at start -> .search() only tries pos 0 -> linear (safe)
RE_WS_END = re.compile(fr'{WSC}*$') # NOT anchored at start -> .search() tries every offset
# selector_iter, lines ~1322-1326
m = RE_WS_BEGIN.search(pattern)
index = m.end(…
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-2026-85999 has been found in soupsieve.
Attackers can target a specific entry point like selector_iter 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-2026-85999" on the vendor's site.
CVE-2026-85999 (soupsieve) — CWE-400 / CVSS v3 5.3
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: selector_iter / RE_WS_BEGIN / RE_WS_END.search / RE_WS_END
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.
A vulnerability (CWE-400) exists in soupsieve. Attackers reach the vulnerable code path via selector_iter without authentication.
Check the vendor advisory for the affected versions of soupsieve. Attack surface: selector_iter / RE_WS_BEGIN / RE_WS_END.search / RE_WS_END.
Severity: Medium (CVSS 5.3/10). Risk of unauthorized operations or information disclosure.
Update to 2.9.0.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
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
-
1Identify 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。 -
2Apply 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。
-
3Post-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
References
- advisory nvd.nist.gov
- advisory github.com
- package github.com
- package pypi.org
- web github.com
- web github.com
- web github.com