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Bug #75807 deflate_init fails with window bits set to 8
Submitted: 2018-01-12 02:09 UTC Modified: 2018-01-12 02:25 UTC
From: matt at bonneau dot net Assigned:
Status: Open Package: Zlib related
PHP Version: master-Git-2018-01-12 (Git) OS:
Private report: No CVE-ID: None
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From: matt at bonneau dot net
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 [2018-01-12 02:09 UTC] matt at bonneau dot net
Newer versions of zlib reject an 8 bit window. Minimum value should be changed to 9 instead of 8. This failure was noticed with zlib 1.2.8.

Test script:
        'window'   => 8,

Expected result:
Expect no output.

Actual result:
Warning: deflate_init(): failed allocating zlib.deflate context in test3.php on line 5


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 [2018-01-12 02:22 UTC] matt at bonneau dot net
Output should actually be:
Warning: deflate_init(): zlib window size (logarithm) (8) must be within 9..15
 [2018-01-12 02:25 UTC] matt at bonneau dot net

"There is a bug in deflate for windowBits == 8 (256-byte window).
As a result, zlib silently changes a request for 8 to a request
for 9 (512-byte window), and sets the zlib header accordingly so
that the decompressor knows to use a 512-byte window. However if
deflateInit2() is used for raw deflate or gzip streams, then there
is no indication that the request was not honored, and the
application might assume that it can use a 256-byte window when
decompressing. This commit returns an error if the user requests
a 256-byte window when using raw deflate or gzip encoding."
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