rijndael_padDecrypt MODE_ECB accepts invalid padLen==0 and rejects valid padLen==16 (asymmetric with CBC path, padding-oracle-prone)
Summary
rijndael-api-fst.c:390-393 MODE_ECB: padLen=block[15]; if(padLen>=16) return BAD_DATA. Accepts padLen=0 (invalid; for(i=16-0=16;...) never iterates; memcpy(outBuffer,block,16-0=16) copies full block; returns 16*numBlocks-0) and rejects padLen=16 (legitimate full-block padding per padEncrypt at :221 which yields padLen in [1,16]). CBC path at :423 correctly uses if(padLen<=0||padLen>16). ECB round-trip fails on whole-block inputs. Padding oracle: attacker flips last-block bytes -> BAD_DATA vs success -> decrypt one byte at a time (Vaudenay). padLen=0 acceptance -> non-error return with attacker-influenced plaintext -> parsing confusion. Fix: if(padLen<=0||padLen>16).
Discussion (0)
PoC verification
Evidence pack
findings/poc/DF-0969 · 2 files| File | Type | Description | Size | |
|---|---|---|---|---|
| fix.diff | suggested-fix | git-apply-able fix for the cited path | 424 B | view raw |
| VERDICT.md | verdict | source-confirmation narrative | 996 B | ↓ raw |
DF-0969 source-confirmation
Verdict: REPRODUCED (source-confirmed)
Impact: none Confidence: likely
Kernel ref: sys/crypto/rijndael/rijndael-api-fst.c:391
Mechanism
padDecrypt ECB accepts padLen==0 (invalid) -> padding-oracle / parsing confusion
Confirmation method
Source-trace confirmed the cited code path matches the finding (exact line/condition
verified against sys/). Runtime PoC not exercised for this source-only Low-severity
item; confirmation is by code inspection.
Recommended fix
See fix.diff in this folder (git-apply-able unified diff).
Phase 8 (combined build)
All 64 fixes were batched into one combined patch
(../_batch/combined_64.patch) and applied to in-guest /usr/src. A single
make -j6 nativekernel KERNCONF=X86_64_GENERIC completed rc=0 with 0 errors under
-Werror (../_batch/fix_build.log, 35374 lines). The GENERIC kernel + all modules
(drm, firewire, usb, netgraph, smbfs, fuse, crypto, vm, pmap) compiled clean.
Fix verification
not_testablenot_testable (source-only): no runtime PoC exercised; fix.diff applies cleanly and the combined single nativekernel build of all 64 fixes completed rc=0 with 0 errors under -Werror (findings/poc/_batch/fix_build.log). Bug source-confirmed in baseline tree. Compile-validation of the fix is the requested Phase-8 deliverable for this batch.
combined build: '=== NK_DONE rc=0 ===' and '>>> Kernel build for X86_64_GENERIC completed on Thu Jul 23 09:17:55 UTC 2026' (0 'error:' lines in 35374-line log).
Confirmed kernel references
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Detail
Exploit chain
none (non-corruption / source-only confirmation; no memory-corruption escalation chain developed for this Low-severity item)
Evidence (decisive lines)
source-only: padDecrypt ECB accepts padLen==0 (invalid) -> padding-oracle / parsing confusion @ sys/crypto/rijndael/rijndael-api-fst.c:391. Combined fix build: '=== NK_DONE rc=0 ===' / 'Kernel build for X86_64_GENERIC completed', 0 errors under -Werror (findings/poc/_batch/fix_build.log).
PoC changes
authored git-apply-able fix.diff targeting the cited line; source-trace verified the vulnerable path. Evidence pack (VERDICT.md, manifest.json, env.txt, fix.diff) in findings/poc/DF-0969/.
Verified recommended fix
reject padLen==0 and padLen>16 (was padLen>=16). matches finding proposal. Full diff in findings/poc/DF-0969/fix.diff.
Verdict
REPRODUCED (source-confirmed). Source-trace confirmed padDecrypt ECB accepts padLen==0 (invalid) -> padding-oracle / parsing confusion at sys/crypto/rijndael/rijndael-api-fst.c:391 against the audited sys/ tree; exact line/condition verified.
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