vulnerability / NVI-00013882 / Revision 2
Soup Sieve: Polynomial-time ReDoS (O(n²)) in the whitespace/comment trimming regex `RE_WS_END` (triggers on VALID selectors)
GitHub lists this reviewed advisory for soupsieve. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
5.3 medium
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
0.609%
FIRST EPSS model v2026.06.15; exploitation probability over 30 days, percentile 0.49159. Missing scores are unknown.
As of · FIRST EPSS
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
soupsieve
source listed< 2.9.0
## 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` ```python
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. FIRST EPSS
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-j934-xhv5-fg8f ↗
GitHub Advisory Database · vendor advisory
Observed . GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.
- CVE-2026-85999 ↗
FIRST EPSS · official catalog
Observed . FIRST EPSS; probability of exploitation in the next 30 days, not local compromise. Dataset date/model retained; FIRST services terms apply.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 2 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.