Skip to content

Reject invalid DEFLATE HLIT values (GH #1368) #1371

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
noloader merged 1 commit into from
Aug 4, 2026
Merged

Reject invalid DEFLATE HLIT values (GH #1368) #1371

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
22 changes: 17 additions & 5 deletions zinflate.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -403,7 +403,17 @@ void Inflator::DecodeHeader()
unsigned int hclen = m_reader.GetBits(4);
unsigned int i = 0;

// RFC 1951 allows HLIT values 0 to 29, encoding 257 to 286 literal/length
// codes. Values 30 and 31 are invalid and can overrun codeLengths below.
if (hlit > 29)
throw BadBlockErr();

const unsigned int literalCount = hlit + 257;
const unsigned int distanceCount = hdist + 1;
const unsigned int codeLengthCount = literalCount + distanceCount;

FixedSizeSecBlock<unsigned int, 286+32> codeLengths;
CRYPTOPP_ASSERT(codeLengthCount <= codeLengths.size());
static const unsigned int border[] = { // Order of the bit length code lengths
16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15};
std::fill(codeLengths.begin(), codeLengths+19, 0);
Expand All @@ -418,7 +428,7 @@ void Inflator::DecodeHeader()
bool result = false;
unsigned int k=0, count=0, repeater=0;
HuffmanDecoder codeLengthDecoder(codeLengths, 19);
for (i=0; i < hlit+257+hdist+1; )
for (i=0; i < codeLengthCount; )
{
k = 0, count = 0, repeater = 0;
result = codeLengthDecoder.Decode(m_reader, k);
Expand Down Expand Up @@ -452,19 +462,21 @@ void Inflator::DecodeHeader()
repeater = 0;
break;
}
if (i + count > hlit+257+hdist+1)
if (count > codeLengthCount - i ||
i > codeLengths.size() ||
count > codeLengths.size() - i)
throw BadBlockErr();
std::fill(codeLengths + i, codeLengths + i + count, repeater);
i += count;
}
m_dynamicLiteralDecoder.Initialize(codeLengths, hlit+257);
if (hdist == 0 && codeLengths[hlit+257] == 0)
m_dynamicLiteralDecoder.Initialize(codeLengths, literalCount);
if (hdist == 0 && codeLengths[literalCount] == 0)
{
if (hlit != 0) // a single zero distance code length means all literals
throw BadBlockErr();
}
else
m_dynamicDistanceDecoder.Initialize(codeLengths+hlit+257, hdist+1);
m_dynamicDistanceDecoder.Initialize(codeLengths+literalCount, distanceCount);
m_nextDecode = LITERAL;
}
catch (HuffmanDecoder::Err &)
Expand Down
Loading