VulnerabilityPublished 13 Nov 2026

CVE-2026-126192: Soup Sieve · General sibling combinator inside :has() matches untrusted HTML in quadratic time

Affects bandcamp-dlSource GCVE Database

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Authoritative record:CVE-2026-126192· Medium 6.3

Not known to be exploited · CVSS 6.3 Medium.

Data as of 13 Nov 2026, 21:02 UTC

CVSS 4.0 base score

6.3Medium

How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none

CVSS scores by source
CNA (GitHub_M)	CVSS 4.0	6.3

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: Present
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: None
Vulnerable system integrity: None
Vulnerable system availability: Low
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: Present: The successful attack depends on the presence of specific deployment and execution conditions of the vulnerable system that enable the attack. These include: a race condition must be won to successfully exploit the vulnerability (the successfulness of the attack is conditioned on execution conditions that are not under full control of the attacker, or the attack may need to be launched multiple times against a single target before being successful); the attacker must inject themselves into the logical network path between the target and the resource requested by the victim (e.g. vulnerabilities requiring an on-path attacker).
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system integrity: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the Vulnerable System are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 12 Nov 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 13 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
Homebrewbandcamp-dl`pkg:brew/bandcamp-dl`Other threats	Affected >=0.0.12	Fixed in–

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Description

## Summary Matching a selector that puts a general-sibling combinator inside `:has()`, such as `div:has(a ~ b)`, against untrusted HTML runs in O(n²) time in the number of sibling elements. A single small document with a few thousand siblings ties the process up for a minute of CPU, so an application that runs a fixed selector of this shape over HTML it doesn't control can be stalled by one request. `:has` is powerful, but much in the same way poor regular expressions can be crafted to cause catastrophic backtracking with greedy capturing, has can be used to create non-ideal scenarios that can cause large portions of the tree to be evaluated for one or many elements if not used thoughtfully. This behavior is not exclusive to Soup Sieve, but browsers make note of these potential performance issues themselves: https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Selectors/:has#performance_considerations. With all of that said, there is room for improvements that can in some cases greatly improve performance. ## Details `:has(a ~ b)` asks "does this element contain an `a` that has a later sibling `b`?". When no `b` is present, soupsieve can't short-circuit, and it answers the question with a nested scan: `match_future_child` walks every candidate `a` under the scope, and for each one the general-sibling branch of `match_future_relations` walks all of that `a`'s following siblings looking for `b`. With n siblings that is (n-1) + (n-2) + ... + 1 comparisons, i.e. O(n²). The adjacent-sibling form `div:has(a + b)` stays linear, because its branch checks only the one immediately following sibling per candidate. So the cost is specific to the general-sibling `~` (and `~` nested inside `:has`), and it shows up on the common case where the right-hand side simply isn't there. ## Proof of concept Installed from PyPI: `pip install soupsieve==2.9.2 beautifulsoup4`. ```python import time import soupsieve from bs4 import BeautifulSoup selector = "div:has(a ~ b)" for n in (1000, 2000, 4000, 8000): html = "<div>" + ("<a></a>" * n) + "</div>" soup = BeautifulSoup(html, "html.parser") start = time.perf_counter() soupsieve.select(selector, soup) print(n, round((time.perf_counter() - start) * 1000), "ms") ``` Measured: ``` n=1000 837 ms n=2000 3667 ms n=4000 14797 ms n=8000 59746 ms ``` Time quadruples for each doubling of n. The n=8000 input is a ~56 KB HTML fragment. ## Impact Availability. Any caller that evaluates a fixed selector containing a general sibling under `:has()` over attacker-controlled markup can be forced to spend minutes of CPU on a small input. The selector is developer-authored and ordinary; the untrusted part is the HTML, which is soupsieve's normal input. A single-pass evaluation of the sibling run (remember whether an `a` has been seen while scanning the siblings once) would make this case linear. ## Mitigation Quadratic time for `:has` in some circumstances is expected and not a bug. While we've made optimizations and there may be more in the future, the way `:has` is designed to operate will never perform in linear time in all circumstances. Users should thoughtfully apply the use of `:has`. The anchor selector (the `A` in `A:has(B)`) should not be an element that has too many children. Additionally, too general an anchor, such as `*`, can cause `:has()` to be applied to every element. Further, it is recommended that the inner selector (the `B` in `A:has(B)`) should use combinators like `>` or `+` to limit traversal. When the selector inside `:has()` is not tightly constrained, Soup Sieve might need to traverse the entire subtree of the anchor element to check the condition. If the risk for a given project is too great, user input can be scanned for usage of `:has` and be denied. Calls can also be wrapped in a timeout to prevent long-running processes as well.

References

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