vulnerability / NVI-00009139 / Revision 1
anacrolix torrent has unbounded recursion in the bencode decoder that causes stack-overflow crash and CPU-exhaustion DoS
GitHub lists this reviewed advisory for github.com/anacrolix/torrent. 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.
6.5 medium
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.
github.com/anacrolix/torrent
source listed< 1.61.1-0.20260911233437-76452a2c8a2f
## Summary anacrolix/torrent's bencode decoder (`bencode/`) applies **no limit on the nesting depth** of nested dictionaries and lists. Two distinct denial-of-service mechanisms follow from that single root cause, both reachable from a single crafted `.torrent` file or from metadata obtained from a peer on a magnet-link/v2 download: 1. **Stack-overflow process crash.** `Decoder.readOneValue` recurses once per nesting level with no depth bound. A `.torrent` whose `info` value is a list nested a few million levels deep (≈8 MB file) drives the recursion past the 1 GiB goroutine-stack limit and the process dies with an unrecoverable `fatal error: stack overflow`. 2. **Quadratic CPU exhaustion.** `metainfo.FileTree.UnmarshalBencode` (BitTorrent v2) re-parses each subtree at every level, making parse time grow ~O(n²). A v2 info dict with a ~30,000-level file tree (≈0.2 MB) takes ~66 s to decode; 60,000 levels exceeds 90 s of decode time. Affected: every application embedding `github.com/anacrolix/torrent` that ingests attacker-supplied metainfo - the CLI tools (`cmd/torrent`, `cmd/torrent2`), any server that opens `.torrent` files, or any client that accepts metadata from a peer for a
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.
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04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
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- GHSA-2wrx-84qj-4pcg ↗
GitHub Advisory Database · vendor advisory
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Public revision history
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- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.