Fix out-of-bounds panic in ber2der on malformed BER input - #94
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`pkcs7.Parse()` could panic with out-of-bounds slice/index reads when given certain tiny malformed BER inputs, instead of returning an error (CWE-125 / CWE-193).
`readObject()` in ber.go guarded its cursor with `offset > berLen` rather than `>=`, letting `offset` reach `berLen` and still pass, so the subsequent `ber[offset]` read one past the end of the slice. The long-form length branch also sliced `ber[offset:offset+numberOfBytes]` with no upper-bound check.
- Change the high-tag-number guards to `offset >= berLen`
- Add an `offset+numberOfBytes > berLen` check before reading the long-form length octets.
Malformed inputs such as {1F 80}, {1F 05}, {30 81}, and {30 84 01} now return an error instead of panicking. Valid BER/DER, including empty definite-length objects and high-tag-number tags, is unaffected.
Add regression tests covering the malformed inputs (via ber2der and the exported `Parse` entry point) and a positive round-trip test for high-tag-number encodings.
alexcottner
approved these changes
Jul 21, 2026
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pkcs7.Parse()could panic with out-of-bounds slice/index reads when given certain tiny malformed BER inputs, instead of returning an error (CWE-125 / CWE-193).readObject()in ber.go guarded its cursor withoffset > berLenrather than>=, lettingoffsetreachberLenand still pass, so the subsequentber[offset]read one past the end of the slice. The long-form length branch also slicedber[offset:offset+numberOfBytes]with no upper-bound check.offset >= berLenoffset+numberOfBytes > berLencheck before reading the long-form length octets.Malformed inputs such as {1F 80}, {1F 05}, {30 81}, and {30 84 01} now return an error instead of panicking. Valid BER/DER, including empty definite-length objects and high-tag-number tags, is unaffected.
Add regression tests covering the malformed inputs (via ber2der and the exported
Parseentry point) and a positive round-trip test for high-tag-number encodings.