Summary
rclone local: crafted Range request against a translated symlink panics (DoS)
When backend/local is used with --links/-l (or the links=true config option), each symlink is exposed as an rclone object whose content is the target path string, suffixed .rclonelink. Object.Open() decodes an incoming fs.RangeOption via Decode(o.Size()), then for a translated-symlink object passes the decoded offset straight into openTranslatedLink, which indexes the target string directly: linkdst[offset:].
RangeOption.Decode's Start >= 0 branch (an ordinary Range: bytes=X- request) sets offset = o.Start with no upper bound, unlike its suffix-range branch (Start < 0, e.g. bytes=-N), which already clamps a too-large value to 0 - the fix for a prior, related crash (issue #6310: "bytes=-90407" against a 5-byte object panicked with "slice bounds out of range", now covered by an existing regression test). The Start >= 0 branch never received the analogous protection.
A Range: bytes=<hugeStart>- request sent to rclone serve http/webdav (or any consumer of lib/http/serve's Object(), which parses and decodes the client's own Range header) against a directory containing a symlink therefore reaches linkdst[offset:] with offset far beyond the target string's length, and Go panics with "slice bounds out of range" instead of returning an empty read.
Details
Vulnerable code (before fix):
func (o *Object) openTranslatedLink(offset, limit int64) (lrc io.ReadCloser, err error) {
linkdst, err := os.Readlink(o.path)
if err != nil { return nil, err }
return readers.NewLimitedReadCloser(io.NopCloser(strings.NewReader(linkdst[offset:])), limit), nil
}
PoC
Called the real production Object.Open() on a translated-symlink object (target length 12) with &fs.RangeOption{Start: math.MaxInt64, End: -1}:
panic: runtime error: slice bounds out of range [9223372036854775807:8]
...backend/local.(*Object).openTranslatedLink
...backend/local.(*Object).Open
Impact
A remote client can send a single crafted Range header against any symlink-backed object exposed by rclone serve http/webdav/etc (backed by backend/local with --links enabled) to deterministically panic the request-handling goroutine. Go's net/http recovers panics per-connection by default, so this fails the one request/connection rather than crashing the whole server process, and no file handle is left open (the panic occurs before any read handle is acquired) - but it is fully deterministic and remotely triggerable with no authentication or race window needed, unlike some other panic-recovery findings.
An arithmetic operation produces a value that exceeds the integer type's maximum, causing it to wrap to an unexpected small value. Typical impact: incorrect size calculations leading to heap overflows or logic errors.
CVE-2026-88015 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.75.1); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Clamp offset to the length of the target string before slicing, matching how a real file read past EOF behaves (an empty read):
if offset > int64(len(linkdst)) {
offset = int64(len(linkdst))
}
Note: the shared RangeOption.Decode() also has a related, unaddressed issue - limit = o.End - o.Start + 1 can itself overflow to a large negative number for a huge End - but a fix attempted there during this investigation broke fs/operations/reopen.go's NewReOpen, which calls Decode with its h.end field still at its zero value at that point in construction. Flagged for awareness but not changed here to keep this patch minimal and low-risk.
Frequently Asked Questions
- What is CVE-2026-88015? CVE-2026-88015 is a medium-severity integer overflow or wraparound vulnerability in github.com/rclone/rclone (go), affecting versions <= 1.75.0. It is fixed in 1.75.1. An arithmetic operation produces a value that exceeds the integer type's maximum, causing it to wrap to an unexpected small value.
- How severe is CVE-2026-88015? CVE-2026-88015 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of github.com/rclone/rclone are affected by CVE-2026-88015? github.com/rclone/rclone (go) versions <= 1.75.0 is affected.
- Is there a fix for CVE-2026-88015? Yes. CVE-2026-88015 is fixed in 1.75.1. Upgrade to this version or later.
- Is CVE-2026-88015 exploitable, and should I be worried? Whether CVE-2026-88015 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-88015 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-88015? Upgrade
github.com/rclone/rcloneto 1.75.1 or later.