vulnerability / NVI-00016112 / Revision 1
Mistune inline_parser: quadratic-time parsing on long runs of `**x**` and `***x***` emphasis pairs
GitHub lists this reviewed advisory for mistune. 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.
7.5 high
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
mistune
source listed< 3.3.0
## Summary **Type:** Algorithmic-complexity DoS in core emphasis parsing. A long sequence of well-formed `**x**` (strong) or `***x***` (strong-emphasis combined) pairs causes O(N²) parser work. Distinct from the bracket-bomb DoS (`[` repetition) and from the formatting-plugin DoS (`~~`/`==`/`^^`); this one fires on default-config mistune with no plugins required. **File:** `src/mistune/inline_parser.py` lines 41-48 (the `EMPHASIS_END_RE` family) and the surrounding emphasis dispatch. **Root cause:** for every opening run of `*`s the parser scans forward using one of `EMPHASIS_END_RE['*']` / `['**']` / `['***']` to find the matching close. Each scan is bounded per call, but the parser invokes the scan from every potential start position. For input shaped `**x**` repeated N times, every `**` is treated as a potential start, each scan can cover up to the end of input. Total work is O(N²). The triple-emphasis variant `***x***` is slightly worse due to the extra alternation between `*`, `**`, and `***` close patterns. Reproducible against default mistune with no plugins. ## Affected Code **File:** `src/mistune/inline_parser.py`, lines 41-48. ```python EMPHASIS_END_RE = { "*": re
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. GitHub Advisory Database
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-4j32-57v6-6g45 ↗
GitHub Advisory Database · vendor advisory
Observed . GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.