[media-types] Request for review of Media Type application/lzip
Antonio Diaz Diaz <antonio@gnu.org> Thu, 10 October 2019 20:32 UTC
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Subject: [media-types] Request for review of Media Type application/lzip
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Dear media types experts, I'm about to submit an Internet Draft of an informational RFC with the specification of the lzip format and an IANA Considerations section requesting the registrations of the Media Type 'application/lzip' and the Content Type 'lzip'. I'm posting the IANA part of the draft here for review. Thanks. The type is "widely" deployed. Most archivers support the lzip format. Many browsers and package managers support the media type as application/x-lzip. The IANA Time Zone Database[1] is distributed in lzip format (and the IANA server identifies the tar.lz files as application/x-lzip). [1] http://www.iana.org/time-zones At least one application (GNU Wget2) is implementing 'lzip' as a content coding for http. In fact the maintainers of Wget2 suggested me to register the type, which would perhaps minimize the work required in the future to deprecate the unregistered type application/x-lzip. I learned about the problems caused by the "x-" prefix at http://tools.ietf.org/html/rfc6648#appendix-B Thank you very much, Antonio. Your Full Name: Antonio Diaz Diaz Your E-mail: antonio@gnu.org 4.1. The 'application/lzip' Media Type The 'application/lzip' media type identifies a block of data that is compressed using lzip compression. The data is a stream of bytes as described in this document. IANA has added the following to the "Media Types" registry: Type name: application Subtype name: lzip Required parameters: N/A Optional parameters: N/A Encoding considerations: binary Security considerations: See Section 5 of RFC XXXX (copied below) Interoperability considerations: N/A Published specification: RFC XXXX Applications that use this media type: Any application where data size is an issue Fragment Identifier Considerations: N/A Restrictions on Usage: N/A Provisional Registrations: N/A Additional information: Deprecated alias names for this type: application/x-lzip Magic number(s): First 4 bytes (0x4C, 0x5A, 0x49, 0x50) File extension(s): .lz .tlz Macintosh File Type Code(s): N/A Object Identifier(s) or OID(s): N/A Intended Usage: COMMON Other Information & Comments: See [LZIP] (copied below) Author: Antonio Diaz Diaz Change Controller: IETF 4.2. Content Encoding IANA has added the following entry to the "HTTP Content Coding Registry" within the "Hypertext Transfer Protocol (HTTP) Parameters" registry: Name: lzip Description: A stream of bytes compressed using lzip compression Pointer to specification text: RFC XXXX 5. Security Considerations Lzip is a compressed format. Decompression of the data may expand it to a size more than 7000 times larger, risking an out-of-memory or out-of-disc-space condition. Since both the gzip and lzip formats contain a single data stream, any steps already taken to avoid such attacks on application/gzip should also work on application/lzip. One possible measure, already implemented in some applications, is to set a limit to the decompressed size and stop the decompression or warn the user if the limit is surpassed. This media type does not employ any kind of "active content", but it can be used to compress any other media type (for example application/postscript) which could then be interpreted by the application. A lzip stream does not store any metadata. Any data appended to the end of the stream is easily detected, and an error can be signaled. It is not apparent how this media type could be used to help violate a recipient's privacy. The lzip media type does not need itself any external security mechanisms. But again, it can be used to compress other media types requiring them (for example a media type defined for storage of sensitive medical information). Because of the nature of the decoding algorithm used by lzip, it is easy to protect the decoder from invalid memory accesses caused by corruption in the input data (intentional or not). Size limits need to be checked at just one place in the decompressor (the decoding of rep0) to prevent buffer overflows. This has been extensively tested with a specialized tool (unzcrash) distributed with the lziprecover tool. The lzip data stream does not contain any size fields that can be faked to be smaller than the actual decompressed data in an attempt to trigger a buffer overflow. (The 'Data size' field in the lzip trailer is only used to verify the size of the data produced as an error detection measure). 6.1. Normative References [LZIP] "Lzip", <http://www.nongnu.org/lzip/lzip.html>.
- [media-types] Request for review of Media Type ap… Antonio Diaz Diaz
- Re: [media-types] Request for review of Media Typ… Antonio Diaz Diaz