Merge bitcoin/bitcoin#36151: makeseeds: fix off-by-one in field count check
What the developer wrote
Authored by merge-script
Merge bitcoin/bitcoin#36151: makeseeds: fix off-by-one in field count check
c786052865fd173fd8bc7396e1303f7840c5b0da makeseeds: fix off-by-one in field count check (aman21-droid)
Pull request description:
Fixes #36146.
`parseline()` checks that a line has at least 11 whitespace-separated fields:
```python
if len(sline) < 11:
# line too short to be valid, skip it.
return None
```
but it later reads `sline[11]` (the user agent), which needs 12. A line with exactly 11 fields got past the check and then raised `IndexError`, aborting the whole run instead of skipping that line. 11 is the highest index the function uses, so the check now requires 12 fields.
This isn't only theoretical: README.md builds seeds_main.txt by appending one crawler's output onto another's, so the file mixes two independently maintained formats, and a truncated download leaves a short last line too. Skipping the line is what the check was already trying to do.
ACKs for top commit:
maflcko:
lgtm ACK c786052865fd173fd8bc7396e1303f7840c5b0da
l0rinc:
ACK c786052865fd173fd8bc7396e1303f7840c5b0da
Tree-SHA512: 3c3aeb8876b7e0eccf8f03faafe0e0bb71d1b11924feaf22b2bb6bf1a36e25bedd622de257060de873c42f12fba8df42d96b2a831a2e8d395220fed70f4bba34
What changed, and why it matters
This is a one-line fix in a Python helper script used to build the list of network seed nodes for Bitcoin Core. The script reads lines of data about internet nodes and was supposed to skip any line that didn't have enough fields. Due to an off-by-one error, a line with exactly 11 fields passed the 'too short' check but then crashed the program when it tried to read the 12th field. The fix simply changes the minimum required field count from 11 to 12. This only affects an offline developer/operations tool and cannot be used to attack the Bitcoin network or wallets directly.
No urgent action required. The fix is correct and should be merged as part of normal maintenance. Operators generating seed lists should use the patched version to avoid build-tool failures on truncated crawler output.
Security signals we found
Off-by-one in input validation guard
IndexError aborts tool run on malformed/truncated input
Fix located in non-runtime, offline seed-generation helper
No memory corruption, privilege escalation, or network exposure
Evidence from the diff
In contrib/seeds/makeseeds.py, parseline() validates input lines by splitting on whitespace and checking len(sline) < 11, but later indexes sline[11] (the user agent field). A line with exactly 11 fields therefore bypasses the guard and raises IndexError, aborting the entire makeseeds run. The patch changes the guard to len(sline) < 12, matching the actual minimum access pattern. The tool is non-privileged, run offline by maintainers to generate src/chainparamsseeds.h, and consumes public crawler data. The crash is a denial-of-service-to-the-build-tool condition, not a network or node vulnerability.
Changed components
contrib/seeds/makeseeds.pyparseline() functionInspect captured patch +1 / −1
### contrib/seeds/makeseeds.py
@@ -62,7 +62,7 @@ def parseline(line: str) -> Union[dict, None]:
# Ignore line that starts with comment
return None
sline = line.split()
- if len(sline) < 11:
+ if len(sline) < 12:
# line too short to be valid, skip it.
return None
# Skip bad results.Why this scored 20/100
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