CVE-2026-49477 | Soup Sieve: Regular Expression Denial of Service (ReDoS) in soupsieve Selector Parser

Soup Sieve is a CSS selector library designed to be used with Beautiful Soup 4. Prior to 2.8.4, the CSS selector parser in soupsieve contains a regular expression vulnerable to catastrophic backtracking when processing an attribute selector with an unterminated quoted value in soupsieve/css_parser.py, allowing an attacker who can supply untrusted CSS selector strings to soupsieve.compile() or Beautiful Soup .select() / .select_one() to cause CPU exhaustion and denial of service. This issue is fixed in version 2.8.4.

Published: 2026-07-14 Last update: 2026-07-21 Assigner: [email protected] Source: [email protected]
NVD Status：Undergoing Analysis，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-49477 is rated Moderate Risk (45.7/100): CVSS High severity, with low exploitation likelihood (EPSS 0.60%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-49477

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-07-15 — 0.60% —

Full EPSS history (1 record total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-49477

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]

Weakness enumeration for CVE-2026-49477

GitHub Security Advisory for CVE-2026-49477

GHSA-836r-79rf-4m37 · Severity: high · Ecosystem: pip — Soup Sieve: Regular Expression Denial of Service (ReDoS) via Selector Parser

OS Trackers for CVE-2026-49477

vendor priority summary link
debian not yet assigned CVE-2026-49477 not yet assigned priority: Debian including 1 source packages (soupsieve), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): open 3, resolved 2. https://security-tracker.debian.org/tracker/CVE-2026-49477
redhat high — https://access.redhat.com/security/cve/CVE-2026-49477
suse high — https://www.suse.com/security/cve/CVE-2026-49477/
ubuntu medium CVE-2026-49477 medium priority: Ubuntu including 1 source packages (soupsieve), 5 status rows across 5 suites (focal, jammy, noble, resolute, upstream): needs-triage 5. https://ubuntu.com/security/CVE-2026-49477

Affected software / configurations for CVE-2026-49477

Vendor Product Version Raw CPE
No affected products in dataset.

References for CVE-2026-49477

cvelogic Threat Intelligence