[Group.of.nepali.translators] [Bug 1647467] Re: InRelease file splitter treats getline() errors as EOF

[Launchpad Bug Tracker]

This bug was fixed in the package apt - 1.4~beta2

---
apt (1.4~beta2) unstable; urgency=high

  [ John R. Lenton ]
  * bash-completion: Only complete understood file paths for install
(LP: #1645815)

  [ Julian Andres Klode ]
  * SECURITY UPDATE: gpgv: Check for errors when splitting files (CVE-2016-1252)
Thanks to Jann Horn, Google Project Zero for reporting the issue
(LP: #1647467)
  * gpgv: Flush the files before checking for errors

 -- Julian Andres Klode   Thu, 08 Dec 2016 15:21:16
+0100

** Changed in: apt (Ubuntu Zesty)
   Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/1647467

Title:
  InRelease file splitter treats getline() errors as EOF

Status in apt package in Ubuntu:
  Fix Released
Status in apt source package in Trusty:
  Fix Released
Status in apt source package in Xenial:
  Fix Released
Status in apt source package in Yakkety:
  Fix Released
Status in apt source package in Zesty:
  Fix Released

Bug description:
  We have just been made aware of a security bug upstream that affects
  the validation of signatures on InRelease file. This bug is to track
  progress for it.

  It allows for attacking a repository via MITM attacks, circumventing
  the signature of the InRelease file.

  It works by making a call to getline() fail with ENOMEM, which is not
  documented as an error for that but follows from the fact that
  getline() can allocate memory. In such a case, apt would treat the
  first part of the file as a valid release file.

  
  = Original bug report =
  From: Jann Horn 
  To: secur...@debian.org
  Cc: 
  Date: Mon, 5 Dec 2016 18:33:09 +0100
  Subject: apt: repository signing bypass via memory allocation failure

  == Vulnerability ==
  When apt-get updates a repository that uses an InRelease file (clearsigned
  Release files), this file is processed as follows:
  First, the InRelease file is downloaded to disk.
  In a subprocess running the gpgv helper, "apt-key verify" (with some more
  arguments) is executed through the following callchain:

  gpgv.cc:main -> pkgAcqMethod::Run -> GPGVMethod::URIAcquire
    -> GPGVMethod::VerifyGetSigners -> ExecGPGV

  ExecGPGV() splits the clearsigned file into payload and signature using
  SplitClearSignedFile(), calls apt-key on these two files to perform the
  cryptographic signature verification, then discards the split files and only
  retains the clearsigned original. SplitClearSignedFile() ignores leading and
  trailing garbage.

  Afterwards, in the parent process, the InRelease file has to be loaded again
  so that its payload can be processed. At this point, the code
  isn't aware anymore whether the Release file was clearsigned or
  split-signed, so the file is opened using OpenMaybeClearSignedFile(), which
  first attempts to parse the file as a clearsigned (InRelease) file and extract
  the payload, then falls back to treating the file as the file as a 
split-signed
  (Release) file if the file format couldn't be recognized.

  The weakness here is: If an attacker can create an InRelease file that
  is parsed as a proper split-signed file during signature validation, but then
  isn't recognized by OpenMaybeClearSignedFile(), the "leading garbage" that was
  ignored by the signature validation is interpreted as repository metadata,
  bypassing the signing scheme.

  It first looks as if it would be impossible to create a file that is 
recognized
  as split-signed by ExecGPGV(), but isn't recognized by
  OpenMaybeClearSignedFile(), because both use the same function,
  SplitClearSignedFile(), for parsing the file. However, multiple executions of
  SplitClearSignedFile() on the same data can actually have different non-error
  results because of a bug.
  SplitClearSignedFile() uses getline() to parse the input file. A return code
  of -1, which signals that either EOF or an error occured, is always treated
  as EOF. The Linux manpage only lists EINVAL (caused by bad arguments) as
  possible error code, but because the function allocates (nearly) unbounded
  amounts of memory, it can actually also fail with ENOMEM if it runs out of
  memory.
  Therefore, if an attacker can cause the address space in the main apt-get
  process to be sufficiently constrained to prevent allocation of a large line
  buffer while the address space of the gpgv helper process is less constrained
  and permits the allocation of a buffer with the same size, the attacker can 
use
  this to fake an end-of-file condition in SplitClearSignedFile() that causes 
the
  file to be parsed as a normal Release file.

  A very crude way to cause such a constraint on a 32-bit machine is based on
  abusing ASLR. Because ASLR randomizes the address space after each execve(),
  thereby altering how much contiguous 

[Group.of.nepali.translators] [Bug 1647467] Re: InRelease file splitter treats getline() errors as EOF

[Launchpad Bug Tracker]

This bug was fixed in the package apt - 1.0.1ubuntu2.17

---
apt (1.0.1ubuntu2.17) trusty-security; urgency=high

  * SECURITY UPDATE: gpgv: Check for errors when splitting files (CVE-2016-1252)
Thanks to Jann Horn, Google Project Zero for reporting the issue
(LP: #1647467)

 -- Julian Andres Klode   Thu, 08 Dec 2016 15:31:29
+0100

** Changed in: apt (Ubuntu Trusty)
   Status: New => Fix Released

-- 
You received this bug notification because you are a member of नेपाली
भाषा समायोजकहरुको समूह, which is subscribed to Xenial.
Matching subscriptions: Ubuntu 16.04 Bugs
https://bugs.launchpad.net/bugs/1647467

Title:
  InRelease file splitter treats getline() errors as EOF

Status in apt package in Ubuntu:
  Fix Committed
Status in apt source package in Trusty:
  Fix Released
Status in apt source package in Xenial:
  Fix Released
Status in apt source package in Yakkety:
  Fix Released
Status in apt source package in Zesty:
  Fix Committed

Bug description:
  We have just been made aware of a security bug upstream that affects
  the validation of signatures on InRelease file. This bug is to track
  progress for it.

  It allows for attacking a repository via MITM attacks, circumventing
  the signature of the InRelease file.

  It works by making a call to getline() fail with ENOMEM, which is not
  documented as an error for that but follows from the fact that
  getline() can allocate memory. In such a case, apt would treat the
  first part of the file as a valid release file.

  
  = Original bug report =
  From: Jann Horn 
  To: secur...@debian.org
  Cc: 
  Date: Mon, 5 Dec 2016 18:33:09 +0100
  Subject: apt: repository signing bypass via memory allocation failure

  == Vulnerability ==
  When apt-get updates a repository that uses an InRelease file (clearsigned
  Release files), this file is processed as follows:
  First, the InRelease file is downloaded to disk.
  In a subprocess running the gpgv helper, "apt-key verify" (with some more
  arguments) is executed through the following callchain:

  gpgv.cc:main -> pkgAcqMethod::Run -> GPGVMethod::URIAcquire
    -> GPGVMethod::VerifyGetSigners -> ExecGPGV

  ExecGPGV() splits the clearsigned file into payload and signature using
  SplitClearSignedFile(), calls apt-key on these two files to perform the
  cryptographic signature verification, then discards the split files and only
  retains the clearsigned original. SplitClearSignedFile() ignores leading and
  trailing garbage.

  Afterwards, in the parent process, the InRelease file has to be loaded again
  so that its payload can be processed. At this point, the code
  isn't aware anymore whether the Release file was clearsigned or
  split-signed, so the file is opened using OpenMaybeClearSignedFile(), which
  first attempts to parse the file as a clearsigned (InRelease) file and extract
  the payload, then falls back to treating the file as the file as a 
split-signed
  (Release) file if the file format couldn't be recognized.

  The weakness here is: If an attacker can create an InRelease file that
  is parsed as a proper split-signed file during signature validation, but then
  isn't recognized by OpenMaybeClearSignedFile(), the "leading garbage" that was
  ignored by the signature validation is interpreted as repository metadata,
  bypassing the signing scheme.

  It first looks as if it would be impossible to create a file that is 
recognized
  as split-signed by ExecGPGV(), but isn't recognized by
  OpenMaybeClearSignedFile(), because both use the same function,
  SplitClearSignedFile(), for parsing the file. However, multiple executions of
  SplitClearSignedFile() on the same data can actually have different non-error
  results because of a bug.
  SplitClearSignedFile() uses getline() to parse the input file. A return code
  of -1, which signals that either EOF or an error occured, is always treated
  as EOF. The Linux manpage only lists EINVAL (caused by bad arguments) as
  possible error code, but because the function allocates (nearly) unbounded
  amounts of memory, it can actually also fail with ENOMEM if it runs out of
  memory.
  Therefore, if an attacker can cause the address space in the main apt-get
  process to be sufficiently constrained to prevent allocation of a large line
  buffer while the address space of the gpgv helper process is less constrained
  and permits the allocation of a buffer with the same size, the attacker can 
use
  this to fake an end-of-file condition in SplitClearSignedFile() that causes 
the
  file to be parsed as a normal Release file.

  A very crude way to cause such a constraint on a 32-bit machine is based on
  abusing ASLR. Because ASLR randomizes the address space after each execve(),
  thereby altering how much contiguous virtual memory is available, an 
allocation
  that attempts to use the average available virtual memory should ideally 
succeed
  50% of the time, resulting in an upper limit of