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Debian LinuxOperating system · Debian

CVE-2017-1000257

CRITICAL · 9.1 CVSS v3.1 Published 2017-10-31
Fix available
A fix is available. Upgrade to after 7.56.0 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
An IMAP FETCH response line indicates the size of the returned data, in number of bytes. When that response says the data is zero bytes, libcurl would pass on that (non-existing) data with a pointer and the size (zero) to the deliver-data function. libcurl's deliver-data function treats zero as a magic number and invokes strlen() on the data to figure out the length. The strlen() is called on a heap based buffer that might not be zero terminated so libcurl might read beyond the end of it into whatever memory lies after (or just crash) and then deliver that to the application as if it was actually downloaded.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

In libcurl's IMAP handling, when a FETCH response indicates zero bytes of data, libcurl passes a pointer with size zero to the deliver-data function. This function incorrectly treats zero as a magic value and calls strlen() on the (possibly non-null-terminated) heap buffer to determine length, causing an out-of-bounds read into adjacent memory. This leaked memory is then delivered to the application as if it were legitimately downloaded data.

MitigationUpgrade libcurl to the version containing the fix (likely 7.56.0 or later). If upgrading is not immediately feasible, disable IMAP protocol support in applications using libcurl if not required.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Debian LinuxOperating system
Affected:= 8.0= 9.0
LibcurlApplication
Affected:>= 7.20.0, <= 7.56.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check installed libcurl version
    Run 'curl --version' or check via package manager: 'dpkg -l | grep libcurl' on Debian/Ubuntu, 'rpm -q libcurl' on RHEL/CentOS, or 'pkg info libcurl' on FreeBSD
    Affected if The reported version is >= 7.20.0 and <= 7.56.0
  2. Identify IMAP protocol usage
    Audit application configurations, logs, or network monitoring for connections to IMAP ports (143, 993) or URL strings starting with 'imap://' or 'imaps://'
    Affected if Any application or service is configured to retrieve email via IMAP using libcurl
  3. Verify IMAP support is loaded
    Check application binaries or scripts that invoke libcurl for IMAP functionality. On Linux, use 'ldd' on the application binary and grep for libcurl, then review application behavior for IMAP operations
    Affected if The application linking against libcurl performs IMAP FETCH commands

You are affected if your installed libcurl version falls within 7.20.0 through 7.56.0 AND any application uses libcurl to handle IMAP protocol responses, allowing potential memory disclosure to the application layer.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to a release after 7.56.0
Interim mitigation

Upgrade libcurl to the version containing the fix (likely 7.56.0 or later). If upgrading is not immediately feasible, disable IMAP protocol support in applications using libcurl if not required.

Recommended fix High confidence

libcurl 7.56.1 or later (Debian: install latest available security update via apt-get update && apt-get upgrade)

  1. 1. Identify the current libcurl version installed: dpkg -l | grep libcurl or curl --version
  2. 2. For Debian 8 (Jessie), update the package list: apt-get update
  3. 3. Apply the security update for libcurl: apt-get install libcurl4-gnutls-dev (or libcurl4-nss-dev depending on your SSL backend)
  4. 4. Verify the updated version: dpkg -l | grep libcurl
  5. 5. Test curl functionality to ensure the update works correctly: curl --version
  6. 6. Restart any services that use libcurl to ensure they load the new version
Caveat Minimal risk; this is a security patch. However, test critical IMAP-related functionality after upgrading as the memory handling behavior may change.

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Debian Linux Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,860
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2017-1000257 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data